You can buy Bentonite and psyllium at many health food stores. I live in a very rural area, and have to order on-line. I buy Yerba Prima products at LAVitamin.com. Their prices are very low, but you have to order a minimum of $30.00. I also buy Smooth Move laxative tea and Parastroy parasite cleanses from them, so its pretty easy to spend the $30.00.
Plan on doing the shakes for at least two weeks for a serious colon cleanse. It often takes months to pass mucoid plaque. I try to do about two weeks a month then take a break.
I use the standard 1 teaspoon psyllium powder to a glass of water, the drink another glass of water. Instructions are on the labels. You can take 1-4 psyllium drinks a day, but start out slowly to avoid constipation. I drink almost a gallon of filtered water every day when doing a bowel cleanse.