http://mynationalreia.com/clubportal/795files/directory.cfm?clubID=795&pubmenuoptID=11912
Use the above link to find a REIA in your local area.
Also, as already mentioned, craigslist is pretty good. I agree with the fake ads, but even putting ads in the Real Estate Services section seeking sellers, can find you buyers as well. This is because people like rehabbers, know this is where wholesalers advertise a lot in. I had 2 email me this morning in fact.
Also, put the word out there to to real estate agents/brokers. They are also a good course for both sellers and buyers! They might know of a seller that is DESPERATE but know they cannot get the property sold, but they can make a little $$$ by referring the client to you. Also, they might have some connections to cash buyers as well. Never know.