So, my local old-school computer shop supplied me with some really nice old IBM keyboards today. They appear to be basically brand new. They had a little bit of what I'd call "storage residue" on them, but they are free of the usual grime that a used keyboard has. No Dorito crumbs in between the keys or grungy looking key caps.
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The one with the box (the larger one) is an IBM 6323 from 1996, which is apparently a rubber dome style keyboard but is one of the better ones out there. I guess its the same as a Chicony 6323, which I've read is a very good keyboard. After a little bit of cleaning, it looks nearly perfect with only a little bit of discoloration along the bottom edge.
The other is an IBM\Lexmark Model M2 from 1993, which had a little bit of gunk on it but looks to have never actually been used. After cleaning it up, its pristine! The legs had actually never even been propped up (the plastic had no grooves in it and it was super tight). And it has that oh-so-glorious super loud springy click that I was hoping for. Its basically the perfect retro keyboard for me because its so compact.
I paid $20 each for them, which isn't an amazing amazing deal (when he told me about them, I thought maybe he had some original Model Ms for the same price) but is good none the less, since I can use them. My Keytronic AT\XT switchable keyboard can now be switched back to XT and used exclusively with my upgraded 5150.