You can purchase psyllium and liquid Bentonite in most health food stores. Yerba Prima makes both...Great Plaines Detox liquid Bentonite and powdered or whole husk psyllium (doses vary depending on which form you use). Sonne's also makes both...the liquid Bentonite is called #7 Detoxificant, but I can't remember what they call their psyllium. You can run a search for Yerba Prima or Sonne to learn more.
Another good Colon Cleanse that doesn't use bentonite...just psyllium and herbs is Holistic Horizons...they have there own website with lots of info.