I'm not certain if you are looking for used books to re-sell? IME, people often want to declutter books. You could advertise for donations - either on Craigslist or in local newspapers or just posting notices on local bulletin boards (you'll often find notice boards at schools and in grocery stores) . Otherwise:
-It's spring where we live, and that means yard sales - always a good source for very cheap books and magazines.
-Church rummage sales.
-Goodwill or other donation shops
-My local public library branch has a table of "withdrawn" books (no longer on loan) that are sold at low cost - 25 cents for a paperback and $1.00 for a hard cover.
ETA: BTW, since I'm not sure exactly about your intentions, I'll just mention that there are concerns about re-selling used books and whether it is fair to the authors.
Edited by ollyoxenfree - 4/3/12 at 1:31pm
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