I’ve used a variety of vendors over the years, depending on their stock. Andy is really top tier in the U.S. but slow and does not handle certain tubes. He is the gold standard. Brendan Bievers was great but his stock seems to be vastly depleted. I think Tube Monger is now gone. I’ve bought some rare tubes from other audiophile collectors who were savvy enough to buy rare tubes when they were readily available. Now, things like real GEC KT 66 power tubes are pretty much impossible to find as never used; ditto GEC U-52 cup bottom rectifiers as NIB.
I run 6h30s in my line stage and finding early DR Reflecktors is nigh on impossible; they are counterfeited and many of those for sale are late production, which doesn’t have the mojo of the early production.
I buy my amp tubes (except for the 12ax7) from Lamm. I can still get Dutch old stock tubes from Allnic for my phono stage main board (that’s where I use the vintage GEC rectifier in the power supply).
So-called "NOS" is typically a "pull" and there is a difference-- a true, never used old stock small tube can last a long time- the pulls are good for a couple years, if that.
If you find a reliable vendor, buy. These older tubes are getting harder and harder to source.
