Actually a company called Cripple Creek in KC. It was really cheap too, i think i may have spent 10 dollars. I went to the bargain bin where they only had a pallet of rock left and picked pieces off. Just bring a couple five gallon buckets to make it easier to haul home.
If you haven't been its definitely worth the trip.
http://www.cripplecreekrockcompany.com/ 