If you're going to mail it, here is my short list in order of my opinion of quality (lowest to greatest):
Thermal Tech (and other local-ish places like them)
Jet Hot
HPC
Swain Tech

I'm probably forgetting someone else too..
Oh, and Zircotec if they were in this country.

Any of those companies will work fine for a naturally aspirated manifold, and you'll probably get the best prices at Thermal Tech.