I've gotten the majority of my stuff off of newsgroups. If you've got the money I'd suggest subscribing to EasyNews or
GUBA (where, according to Alex's sig, "You can find anything there"

).
As for p2p, I'm currently using Shareaza, but it's a lot of time, patience and luck to find anything decent. P2P was a lot easier before spammers/spyware/etc

. Here are a few general suggestions though:
- use your filters; if you're looking for "flashing" filter out "mardi gras" (how you filter depends on your p2p program)
- check the size of the files being returned on your search; files <100kB in size usually aren't worth it, and files of EXACTLY the same size are most likely the same file despite being named differently; if you can, set a size range to help narrow your searches (eg. 1-5MB, 5-10MB, etc)
- avoid file names like "xxx upskirt sex porn celeb..." and so on.
- have patience when d/l a file; The one guy who has a legitimate file you're looking for may be on a 14.4kb dial-up modem with 20 other people d/l from him.
Also, check out
http://www.zeropaid.com/ they have info, news, and forums on all sorts of p2p stuff.
Don't be to surprised if not too many people respond to this. If too many people give away their secret fishing spots, there'll be no more fish to catch

.
Hope that helped.