Tube vendors.

I get mine from The Tube Store. The first I tried, they seem to be pretty quick and reliable. I have ordered at least a half a dozen times.

I deal almost exclusively with Kevin at Upscale Audio, but a lot of people recommend Jim McShane.

http://www.mcshanedesign.net/tubes.htm

Also, Brent Jessee and Andy at Vintage Tube Services.

https://www.audiotubes.com/

http://vintagetubeservices.com/

jim m is very good with testing and supplying modern power tubes - he is not really an active chaser of old rare small signal tubes - he may have some occasionally but he is not like andy baumann or brent jessee who will vigorously chase estate sales and do laborious sorting and testing of old rare tube collectors that have passed or are emptying their stocks due to age

kevin started travelling all over the world chasing good old stock tubes he has quite a stash he is selling down over time

i don’t know as much about the tube store but they also seem to have some old stock tubes as well, and they also seem to have a rigorous test regimen

for good, now increasingly rare small signal tubes and rectifiers i would say andy @ vts, brent jessee and k deal are best, they test and they still have decent supply and variety - of course you will pay through the nose for the rare good stuff, for some tube types the cost is still fairly reasonable

I use Tube Depot. Very knowledgeable sales force and to boot they sell great BBQ sauce!
https://tubedepot.com/