You'll be able to find clay. Should have at one, maybe 2 out of the following 3: Meguires, Mothers, and Claymagic.
For Meg's DACP or any other serious cleaner/polish, a good autobody supply and/or automotive paint store should have it.
NAPA auto parts may also carry DACP, but should also carry the 3M and Duragloss line of polishes. I haven't heard anything about Duragloss (search here on Autopia - I'm sure someone has), but I have heard good things about 3M products (again, search here). Most of my experience is with Meg's products.