I don't think there was a dedicated one then (at least I never took time to look for them when I was a teen, more focused on whatever piqued my interest at that point) but you could find people requesting and filling requests for them throughout alt.binaries.pictures.erotica and associated subgroups. My teens were mid-late 90s.

I just googled and see there is an a.b.p.e.upskirts one now, but I don't know when that was created. Could've been there all the while.