Can be obtained from drilling supply companies in a pinch. Or you can obtain more specialized bentonites such as calcium montmorillonite. Some bentonites are good for taking internally for detox. There are apparently magnetic clays as well which have more drawing power. To my knowledge, bentonite goes negative when wet and has a pull on ions.
Regarding clays perhaps see:
http://www.tuberose.com/Detoxification.html (scroll down to the section about clays);
http://www.eytonsearth.org/
Also, you might contact
American Colloid via email or telephone to ask them the price on clays if you want bulk (50lbs...200 lbs..a ton...).
Clay baths or epsom salt + baking soda baths can also help with radiation detox.
Dont overlook Pascalite for internal use (not cheap and not necessarily readily available in bulk).
The point here, if a nuke goes off, radioactive materials can apparently be removed from the body with clays just like other toxins and heedless suffering need not be experienced--not to mention the buffering properties of the bentonite.
On a detox note, the difference between certain clays and activated charcoal is that while both activated charcoal and clay can detox, clay has more pulling power and the right kind of clays can provide nutrients in the process of pulling out toxins (apparently even heavy metals/lead).
So even if one doesnt coat one's skin with the clay, it'd probably be a good idea to take a clay bath or take it orally in small quantities. Believe it or not, I sometimes sprinkle clay on salads (if available handy)--pascalite preferred. Still, in the event of a 'nuclear event' I'd prefer full or almost total body coverage over just a bath. Alternatively in a pinch one could make a 5" x 5" or larger poultice or w/e its called : filtered water + clay over a cotton gauze then covered with plastic (saran wrap) and taped to the skin (clay on skin) with surgical medical tape ...it could be put under the shirt and still to my knowledge would have potency in drawing out toxins, radiocative substances.
Also, to my knowledge epsom salt + baking soda + capful of hydrogen peroxide in a bath can help with detox/radiation exposure.
Clay pudding anyone?