I’ve been running tubes since about 1973. I used to retube my ARC SP 3-a-1 with period Telefunken 12ax7s which were about 10 bucks a tube. Finding true unused ones from the ’60s or ’70s is not impossible but they are expensive now.
Everything I run is tubes except for the home theater. (Even that was three ARC tube amps at one point until I decided it was stupid).
My vintage system uses a matched quad of GEC KT66s from the era. Not easy to find and if and when, might have to be replaced with a modern production tube.
The line stage in the main system only likes period DR 6h30s, a tube that is very scarce.
The rest I source from Lamm (for the amps), Allnic (replaced all the audio circuit tubes with Holland Siemens). I roll the rectifier in that, and have a bunch of grail tubes- I like the GEC u-52 in my system, given how it voices.
I’m no tube guru. I rely on trusted vendors. Andy is the best, but he’s slow and old school. I’m not buying bulk- but want enough to have back ups.
Tubes are truly a pain in the ass these days, given sonics. More power to you if your gear sounds good on modern production tubes. I’ve found that I do better with other, older tubes, and that’s where you wind up going down the rabbit hole.