At this point we're just anecdote vs anecdote, but I've been pleasantly surprised during most of my attempts.
I'm not going to try and sift through collections on abandonware sites and try to cross reference them against known copies sold. The only person who can speak to your personal white whale is you.
archive.org has many gigs worth of 90s era "900 in 1" shareware/freeware CDs on it. Games that never sold copies and were just stolen personal projects shoved onto one disc.
Recently I found multiple users on SoulSeek that collectively have nearly the whole discography of a relatively unknown japanese house music label, Far East Recordings. The main artist Soichi Terada's work on the Ape Escape game soundtracks (only thing he's known for in the US) is easily available as are his CD releases, but there's a ton of vinyl only releases (he was prolific in the late 80s through mid 90s) that I could find evidence existed but couldn't actaully find the music anywhere. On top of that he did a lot of collabs with japanese artists that just don't exist online, and I found a ton of their stuff on SoulSeek as well.
Also, be the change. I've backed up all the CDs from my childhood, and put them up on the archive if I couldn't easily find them on it already. When I find time I'll do the same with all the old freeware games I downloaded back in the early 2000's. Keep backups. I've got easily accessible backups going back to my family's Windows XP, and I have our Win 98 drives whenever I decide to buy the right adapters.
Anyway, hope you find what you're looking for.
Oh fuck off. "Then she shouldn't have dressed like that" ass take.