It could be any number of things, a loose wire, loose or faulty connector, loose fuse, faulty ground, or a short. Hope it's not a short, as those can be a PITA to trace down.
As far as vendors, Quadratec is pretty good. I've also used discountjeepparts.com, as well as 4wd.com. The best thing to do, IMO, is to check several sites, to see which has the best deal on the parts you need. As for salvage yards, depends on where you are located and if there are any close by. Your profile says you are in Kansas, so if you aren't that far from Topeka, there is 4x4 Land.