Not sure EXACTLY what you are looking for, but I bought a big bag of red lava rocks from Home Depot for 5 bucks. They are very natural looking, various sizes. You have to rinse the heck out of them though.
1 Gallon Bowl - White/Purple Half Moon Betta
1.5 Gallon - Blue Veil Tail Betta
2.5 Gallon - Red/Blue Veil Tail Betta
2.5 Gallon - Pea Puffer
5.5 Gallon - RCS, Ghost Shrimp, Ember Tetras, Sparkling Gouramis, Bumble Bee Gobies
10 Gallon - Pure Black Bar Endlers
29 Gallon - Planted Community - Cherry Barbs, Neon Tetras, Various Cory Cats, Albino Bristlenose Pleco