I guess you have tried Soulseek? There is a linux (nicotine) and an OS X client (ssX) availible. I have found it to be the best place by far to look for obscure music. You might have to give the search some time though (days) since the user who has the music you want has to be online for it to show up.
And Gemm is a good, although sometimes a bit expensive, place to find second hand Lps and Cds.