Tube Dealers 2021

Audiotubes.com Brent Jesse

Vintagetubeservices.com Andy Bowman

I have had good dealing with:

http://www.triodeelectronics.com/tubes.html (Ned)
https://tubeworldexpress.com (Brenden Biever)

You may also want to try:
https://www.tubesandmore.com 
https://vacuumtubesinc.com
https://www.nosvacuumtubes.net
https://www.jacmusic.com (European)

seta45

Brent Jessee Recording is my go-to, for rare, NOS, 6SN7 Octals.    I've gotten some of my very best NOS, nine-pin miniatures (especially, my Siemens), from this seller, in Germany:   https://www.ebay.com/usr/audiotubes_de?_trksid=p2053788.m1543.l2754          I've never been disappointed by either TC Tubes, or Upscale Audio, when it comes to NOS or new production power tubes (6550, KT88, EL34, etc).        https://tctubes.com/          TC Tubes surprised me, when one of an octet of GE 6550s went bad, after almost two full years of service.   I returned the set to them and they ID'd the offender, found one that matched the remainders and gave it to me, gratis.     Hard to beat that kind of customer service.

I'm not a heavy tube user, but found Ken Chait to be helpful.

https://www.tubeman.com/index.php?l=page_view&p=contact_us

Depends on what you are looking for:

I sell Emission Labs and KR if you are looking for the Czech tubes.  I am one of the only folks who carries KRs whole line here in the US.  

verdantaudio.com

For smaller tubes and NOS, I like the folks at Tube Depot.  I buy from EHX when quantities are a bit larger but I buy from them for small quantities and NOS.