Wes.....
Take a road trip down to Central Texas and you can probably collect your own!! Boutique Pets and The Fish Gallery both have Holey Rock in stock and will probably be cheaper than Dallas North Aquarium. If you don't mind driving as far as New Braunfels...Armke Aquariums down there has lots of the stuff!!! You might also look in the Yellow Pages for Rock/Mineral stores....they're likely to have some too (and maybe cheaper than a pet store).