I bought my first batch from a beauty supply store that was used as facials. My second batch I bought off the internet that sold the stuff by the pound. I finally found some liquid stuff in the health food store and that's what I'm using now.
I also read the ingredients in the leg packing for my race horses, and yes, the main ingredient is the benonite clay. A friend of mine also told me that he uses it for his pipes on his well.
I say if livestock, wild animals and such go out of their way to eat the clay when they are sick, it's good enough for me.