Dubstepforum.com

defected acapellas + torrents
other than that dl slsk and search for a specific song
+ acapella at the end
failing that alot of pop/hip hop/rnd etc cd singles/vinyls come with either acapellas or instrumentals as well as originals on them and with a clean instrumental and clean orig you can diy your own acapella
also acapellas4u.co.uk does kick ass

There's always p2p programs and what not as well, although it depends what time of day and most aren't quality

as to the other people in this thread bitching though..the smart ass shit is really over rated

he could google and go through numerous shit sites in an attempt to find a good one, or he could just post a topic here in hopes that somebody on this forum already knows a good place or technique to get them?

seriously, if you don't have anything positive to contribute there's no point in posting, it's just going to clutter the thread and it'll still be here when you leave regardless..

also theres plenty of older akai sample cds chock full with royalty free acapella bits
http://www.myspace.com/deadlyhabit
tune synesthesia for example vox were all put together off an old akai cd