Landscape supply store. If you live on the east coast I don't think you'll find it in bulk. I need 5 cft and couldn't find that. I've looked extensively, I've had people in the industry who have looked and told me unless you wanna pay shipping, figure something else out. I think I'm going to go with a mix of lava rock, vermiculite, perlite, maybe some rice hulls too. I was told not to use perlite for living soil bc eventually it all works its way up. I know that happens but I've only seen/ heard about it happening when you drench your soil, for a flush, then the perlite def comes up. But if I'm using blumats in living soil, then hopefully my soil should never be drenched and I'll never lose my perlite. Good luck