Andy is the best I've found for top quality tubes which are truly NOS. He measures every aspect of a tube including noise and microphonics. Brent is great as well but does not test for noise. There is a $10 fee for noise testing, no big deal, just remember to request it especially if purchasing 6SN7's.
Prices have increased dramatically over the past couple of years due to the dwindling supply of new old stock. As whart has mentioned, many so called NOS tubes have been pulled out of a particular device and may even have the original box. An honest dealer will list tubes as "tests as new" and provide test results.