I'm thinking something like this is hopefully close enough, it has to be a non-shiny, non-metallic paint otherwise I think it would stand out against the matte finish of the wheels.
http://shop.hobbylobby.com/products/...-paint-356220/
I'm thinking they should also have some sort of foam applicator or something that's a close match to the size of the grove at Hobby Lobby or Michael's.