There's an obscure Japanese tracker format known as "Ultramarine" (UM). The thing about it is that it stores the samples outside the songs, so they can be reused between songs. I've lost the old archive of music I had in the mid-2000s, and I'm digging it back up now. I've found that I can find a few Ultramarine songs, but the sample bank they were written for wasn't archived.
I've been able to speak to one of the people who composed music in it, but he doesn't seem to have his files anymore and isn't currently focused on his older stuff.
The main pages I've been looking at -
Ultramarine homepage: https://web.archive.org/web/20041203230615/http://www.ultramarine.org/
Suppoko circle homepage: https://web.archive.org/web/20011216215459/http://www7.big.or.jp/~suppoko/
Tan-Y's homepage, with broken download links: https://web.archive.org/web/20041205234556/http://www4.big.or.jp/~tan-y/
Tan-Y's download page, where none of the links were archived: https://web.archive.org/web/20071209004142/http://www4.big.or.jp/~tan-y/download/music.cgi
Gay-LLA's homepage, with working downloads but no sample data: https://web.archive.org/web/20011205210159/http://www2s.biglobe.ne.jp/~GAY_LLA/