OK, I don't know if this post is really acceptable or not, but it seemed to be relevant to the kind of rare releases and versions that people here are looking for, so I'll post it anyway (and delete it soon since it's time-sensitive).
For those of you who are Usenet savvy, there has been a recent posting of a couple compilations of rare, hard-to-find, 12", extended, etc. "alternative" stuff on alt.binaries.sounds.lossless. Specifically the Classic Alternatives ("80's Extended Rare Mixes") and Hardest Hits (as in hard-to-find, not hard-rock, I guess) series.
To address some of the recent concerns here, it seems that at least in the US these appear to be priced as if they are out-of-print themselves. And no "new" purchase options from majors like Amazon, etc. (with my very quick research)
Oh, yeah, I guess these were up earlier in the week, so sorry for being so late; I just noticed them tonight myself.