If you are new to NOS you'll want to spend some money at first to be sure you're really getting a good tube, then learn over time what each brands strenghts are, and eventually shop on your own power, after a few years of this A/B approach using real NOS. If you're smart about NOS you can do well (read: good deals) on Ebay, but this is harder. You will probably get burned a few times as there are some junk tubes on Ebay as well. www.tubeworld.com
- not cheap but reputable Upscale Audio - Rare Tubes
NOS is not dogmatic snobbery, there are some new tubes for guitar amps that are 'good enough' for power tube apps and the occasionally Sovtek or JJ could be just the dirt you need, but for a more open tone that has some real beauty NOS wins most of the time. RCA Black Plates, pre-70s Mullard, Telefunken, Amperex Bugle Boy, even Sylvania for a clean tone, etc. ... each of these has a color that can be useful in a chain.
I have a 22 tube eq and each section uses a different brand in a low noise, matched pair based on that brand's strength (Mullard- Hi Mid boosts, RCA - Low Mids, Telefunken - Hi Shelf, Amperex EF86 Output Gain, etc) ... the difference between this and the stock, select Russian tubes was clear. I paid no more than $25 per tube on Ebay, but that's after 20 years of using tubes. Best to pony up to the dealers that can educate you.