Liquid Bentonite can be found at most health food stores. Yerba Prima Great Plaines Detox and Sonne's #7 Detoxificant are two well-known brands.
There is no harm in taking Bentonite on it's own, but its effectiveness is increased when combined with psyllium which acts as a broom to sweep the loosened material from the intestines.
Here is a link with additional information on bentonite: