If you are planning to build a clay oven and you still don't have materials for it, try calling gravel companies. Some of those stores do retailing or selling small quantities that you only need. You can browse the internet to find a good store that will help you for your project. If some don't have it they will likely recommend you to other store they know who does. If you will keep browsing the internet, you may read in some forums and blogs about the "Cob Builder's Handbook", "Build Your Own Earth Oven", etc. They cover clay and clay mixes very thoroughly. Or if you know any landscapers, they also be able to help yo find what you need.