umm i think petco has some and stone stores would have them probably. If you look hard enough you may find some around you. I mean I live in the upper Chesapeake bay and find them in the river around my house. (although I would never collect them bcuz of mud stuck in them/nasty bacteria) I have lava rocks in my 30 gal. bought at petco but, they are kinda small. I would also make sure you have brown/red substrate as black or white will not look good. They are really cool textured and add a wild accent to my tank. My grandfather got some from hardware stores and other such shops for his nonfunctional retaining wall. They are great pieces and I hope you find some nice stones. Good Luck!