whle Jim specializes in restoring old Citation amps, his tube pages are a good listing of a variety of NOS, used and new production tubes.
I've bought literally dozens of tubes from Jim without a single problem. He tests every tube, and guarantees performance. Plus he's a nice guy too! Hard to beat.
Check out http://pages.prodigy.net/jimmcshane/tubes.htm
I have no other affiliation, just a happy customer.