Ultimately, if you are serious about collecting funk, you are going to have to find stores which sell records exclusively or mail-order services. Several such services exist on the Web. Under these circumstances you will probably be paying considerably more. Consider, though, that you are not leafing through piles of unalphabetized, scratched records hoping to find a funky hit or two. This has all been done for you.
Some stores specialize in funk.
Track these places down, and go nuts. Many funksters love to trade vinyl, as well as live recordings. This is where the Web really comes in handy. A funky album shines out with a particular style. You can safely assume that an album with a picture of five white guys in cowboy hats is probably not a funk album.