Carl Kauffeld successfully used pea gravel (~ 1/4 inch diameter) for the snakes in the Staten Island Zoo. See http://www.nytimes.com/1974/07/11/ar...en-island.html

By the way, Kauffeld's books are great reading.

I have used slightly smaller gravel for some hatchling and juvenile bullsnakes. There was no trouble with impaction, but I did have to stay on top of the spot cleaning. Sand is much more of a problem than gravel for impaction. Sand also traps much more moisture between the grains than gravel, so I do not use sand.

I don't have any places or products to recommend, but an aquarium shop might be worth checking out.

Good luck.