Where would I find white and regular chocolate clay?

You can make it from the wafers. 1 lb. of wafers, melted, + 1/3 cup of corn syrup. Let it sit overnight, wrapped well.
That's it!

Totally serious. Got the recipe right here on CC. Have used it on many cakes. Was great for modeling figures on my jungle safari cake, and I've also rolled it out and done polka dots (mod Monkey cake) It is awesome!
I love it, b/c it tastes much better than fondant.

Wow!!! I can hardly wait to try this! Can this also be used to cover a whole cake? Or, is it just for accents?

Also, online I found one that calls for....

1 16 oz. tub of chocolate frosting
1 cup creamy peanut butter
2 1/2 cups. powdered sugar

Mix it all together on low....Too soft, add more powdered sugar....Too stiff, add a couple more TBSP of peanut butter.

Haven't tried it, but, it too, sounds good!

It can be used to cover a cake, although I've not tried it. There is a bakery that does almost exclusively modeling chocolate to cover cakes - can't rememeber the name. Do a search for 'modeling chocolate' on the forums - someone posted it in another thread. So worth looking for!
Good luck!