Usually people have the opposite problem - they suddenly find themselves in possession of a clay pot for cooking (either through a garage sale or the generosity of relatives) - and have no idea what to do with it.

Clay pots are available at Amazon.com, Cooking.com, Chef's, and a number of other online cookware retailers.

You might have more success in an online hunt if you search for the word Romertopf, the name of the market-leading brand, or something that clearly signals cooking, such as "clay roaster" - otherwise, you mostly tend to find clay flower pots.