My main source for physical copies are local trading sites.

Importing from UK was my second favorite. They have a lot of cheap and good quality games. But they had the great idea of leaving the EU and shipping prices grew 3 times higher and on top of that VAT plus handling fee. They rarely competitive with these extra costs.

Sometimes I buy games from other countries over ebay, but those are mostly very rare games that aren't available as a digital download. Like for example the last two were Wolfenstein from Canada and Prey from I think Ireland.

For PS3 games sometimes buy them from Japan. Some of the games that are expensive in other regions are a lot cheaper there. Though at the same time, not all Japanese releases has options for English language. Same for Bethesda games. I'd love to get a New Vegas Ultimate edition for X360 and last year I got one from a local game shop, but it was a German release and my German language skills barely exceed Mein Leben! and Guten Tag! (learned the basics of the basics as a third language in elementary school 20 years ago).

Otherwise, yeah, GoG is the most convenient source. For certain games the Humble Store also work.

Mostly from GOG, but I do occasionally browse my local classifieds for physical copies.

Of course, original retail releases (especially the big box ones) are fairly expensive, but if you don't mind getting a later re-release, those tend to be really cheap. The downside is, you usually don't get a physical manual and only a flimsy DVD case + discs. But these re-releases often have the manual in PDF form somewhere on the disc, and sometimes also the latest patch as well. So it's a trade off.

Regarding GOG games, their installers don't work under Win9x, but you can usually install the game on your modern PC and just copy over the folder to your retro machine. Sometimes, you also need to delete Glide wrappers and such if you're playing on real hardware.

Digital copies I get from GOG.

Physical copies I obtain via local thrift stores, local ads, or from Ebay. Ebay tends to command a premium, but I have lucked out with occasional deals. I also try to buy within Canada to preserve the localization of physical boxes and manuals, since North American versions typically differ from European ones.

I also have a number of local shops that cater to vintage gaming, but unfortunately none of them carry PC games, just console stuff.

I am more a physical game buyer. I do the rounds of thrifts and yard sales. I see a bit of a selection but only pick up things I like or might play rather than thinking of trades etc. Guess it works out about 3 or 4 a year. I see stuff on classifieds but I have not been tempted by anything yet, pricing around here can be a bit whack, like they want double what you can get it for on eBay or something. Not really bought any on eBay though either. I guess it's much like my hardware, take what's interesting and cheap mode, rather than must have at any cost.

Budget vs Original release... Some things I like about budget releases... fixed and patched mostly, might still need something for less usual hardware, but you don't spend an hour messing with finding updates before you can play. Copy protection is often toned right down, not always though, some few have been shoehorned into publishers latest greatest idea about copy protection badly, while the originals remain sane. But take NFS:PU budget release I've got, also got a bigger box release but it's packed somewhere, it just fills in the serial for you, don't need to be scrabbling in the paperwork. Later releases of Frontier:Elite II had the annoying manual word thing turned off. BUT conversely, they fixed "bugs" that were also highly convenient cheats. So when is the original better, that can be a long string of if this and if that, if it wasn't a buggy mess at release, if it had some nice glossy maps and backstory novellas inside and if they are still there and not lost, then original might be gooderer. However, sometimes these things come later with a special edition in a tin, with bling, and a pony.

Very rarely do I see physical games for sale anymore, so I'm mostly relegated to trolling ebay for auctions that are ending soon or new listings at lower than market average price.
It's gotten much harder the past 3-4 years though.

Computer City
CompUSA
Babbage's
Best Buy
Steam

I used to find them at local thrift stores, but I have not been to one for ages. GOG works for older games.

If I want a physical copy (mostly for collecting's sake) - then it's eBay for me, and like was said - eBay UK in particular is a good source for cheap games, if the shipping is cost is reasonable (sometimes it is, sometimes it isn't).

Digital copies - I don't care about legality. If I want to buy something, I will only buy it from GOG, to show support for their DRM-free game preservation initiative.

A few years ago I was borrowing games from the city's public library. It had a games corner..
Classic games I found there were: Full Throttle (big box), Monkey Island (big box), Monkey Island 3, Toons Truck (big box), The Daedalus Encounter, etc.

For digital copies I mostly rely on GOG and to a lesser extent Steam.

For physical games I haven't found anywhere that's "on demand" for a reasonable price. I have a long wishlist but it's just chance what I can cross off. I've had some good luck with Half Price Books, but that's only helpful if you're in certain parts of the US. There's a few used game stores as well, but my luck has been limited to the occasional small box game. As much as I don't care for the eBay premium I occasionally find half-decent deals.

Love this topic! Just want to chime in that timing is almost as important as finding a game on EBAY. I remember buying Wolf3D ages ago fully boxed with all papers and it was cheap as chips. I think the pandemic (other things too) really broke the metric for the secondary market.

Not 1000% sure about legality but the REMOVED project is a nice archive/collection of games up for grabs

i used to get physical copies new, in used game stores and in charity or flea/yard sales

the observation that there aren't as many around now is true, I've noticed that in the last 5 years - all the same sources exist but the overall volume is dropping it seems

gog is good for older games if you just want them to run on current PCs

Mostly Steam, some gog. I avoid the other platforms to not spread the library even further.
For physical copies of old games, its Ebay, Ebay Kleinanzeigen (German version of Craigslist), and Facebook collectors group.
But prices for these phyiscal copies are getting more and more expensive
Here is my (almost) recent physical collection:
https://www.youtube.com/watch?v=3ZFp8YOwrso

Removed link from post to so called "abandonware", updated topic.

Ebay mostly.

I have a bunch of saved stages for games i can't get on gog. They come up for reasonable prices every now and then.

awesome so many responses. Thank you. It sounds like we're all doing the same things. It seems like everything is drying up. I get lucky every once in awhile but its very rare anymore. As for downloads, how legit is REMOVED? Link below

REMOVED

There is no such thing as legit abandonware. It's just a term for items where someone thinks that it's unlikely that the owner cares enough to sue you. But that doesnt make it legal.
So I am pretty sure that this link will be deleted as well.

Just noticed the thread title edit... Hilarious that it had to be clarified.

The last I picked up old games was at a large indoor flea market. Whatever happened to those? Also, computer shows with all the Chinese knockoffs need to show back up around here. I could really use some cheap cases.