A craft store like Michael's or A.C. Moore is the only place I can think of, but you're better off field stripping it and using a gun cleaning kit. They're relatively cheap depending where you buy it (WalMart, Big Lots, Ollie's, etc.)
Thanks for the suggestions! I guess I should have been more specific. The barrel is welded in place, so I have to go through the holes to clean the gunk off.