If you can get a couple cups/pounds of live sand from your lfs or a friends reef aquarium, that would be great, I think (make sure to check for no aptaisia/hair algae, etc.). That way you would get, hopefully, a mixture of different types/kinds of worms, maybe small snail or two or small starfish or something (I'm talking small, like 1/4 inch in size) if it is a good sand. You can also buy sand or a "replenishing kit" of some sort via the internet, I would think, though, more money.
Frank