eBay seller cold340has a bunch of extremely interesting and very unique items up for sale. Included are several auctions for original 3.5″ development disks and and source code.
None of the auctions are cheap, but there a reasonable price for something this unique. If you’ve got the resources to actually open the files as well, there could be some amazing content on these. Even if you don’t, they’ll make a great conversation piece in your collection.
There are disks for SNES (B.O.B game source among others), Genesis (Spiderman and others) and PS1 disks with a 440 page reference manual.\