Try Brownells, then Gun Parts Co. Smith will likely sell you a barrel also.
I've bought several from gunsmiths or gun shops. Paid $25 for a 19 4" barrel a couple years ago. ask around, you may strike a source for reasonably prices barrels. And check some of the big name shops that do custom PPC or competition guns, they often have piles of them around and will sell them for about half of new price.
