The spacing is just regular 2.54mm. The 16 bit has 49 pairs arranged 31 + 18.

I was able to find some good results when looking for "49 card edge connector" rather than 98, since they're pairs of pins. Including some on ebay. You can check more specs of it here: https://www.te.com/usa-en/product-5645169-2.html

There's not many cheap options that I can see in the UK, but there are some in the US and other countries. I personally have enough dead motherboards that I bought for scrap that I've been desoldering and reusing.

Actually, that's really helpful; I'm getting far more useful results for 49 position than 98. Thanks!

I had to find CAD models of one at the weekend.

I thought it wouldn't be possible, but same as you, searching for 49 instead yielded far better results (for anyone wondering, they can be found here)

Got them. Found a UK supplier that had a handful of the full length 98 way connector and picked up 4 of them for £5 a piece. RS actually has the TE parts available to order... but at a minimum order quantity of 72!

I still need to get a couple of 8bit connectors, but if I don't find any I can always machine one 16bit connector down to the keyway.

Thanks again.

Try searching for "31 card edge connector". It looks like there's some "50-31SN-12" in the states and they look correct for 8-bit ISA.

ISA 16bit
Digikey: A31716-ND
Mouser: 571-5530843-3

ISA 8bit
Digikey: A121053-ND
Mouser: 571-7-5530843-0

Full Length ISA
Digikey: A101941-ND
Mouser: 571-5176139-2