What is it and where do I buy it? I want to mix it with RKT to mold a lighthouse. Thanks everyone for your help.

Make your own candy clay using the recipe listed in the "recipes" tab right here at CC:

http://cakecentral.com/recipes/7425/candy-clay

Very easy and cost effective

thank you, I will do just that.

Here is a thread that just might be the answer you need. It is long, but contains a lot of useful information. (Added bonus: it will give you a good laugh!)
http://cakecentral.com/cake-decorating-ftopict-623004-pepe.html

if you are a visual person here is a tutorial I made for how to make candy clay.