I bought Psyllium husk powder at Whole Foods. Brand name, Yerba Prima. Not expensive. Got powdered Bentonite there too--3-4 dollars.
Drink TONS of water afterwards. I'm trying a little apple cider vinegar in the water following the shakes. I'm doing 2 shakes a day. That seems okay. More than 2 is hard for me to send down the pipes during the day.