bcowen
Headphoneus Supremus
Try these guys...one of the best in the U.S. and they will not rip you off like some on eBay. Roy & Dale are great guys and are always fair and honest. Heck, you can even call them and that is rare these days. Check em out.
https://vacuumtubes.net/
There's also Upscale Audio and Tubeworld in the US. Both are expensive. But you get the real deal, and if there's a problem they'll take care of you. I've purchased numerous times from Langrex in the UK as well with good results every time. He sells on Ebay as well as through a web store. His prices are quite good in most cases for European manufactured tubes.
https://upscaleaudio.com/collections/vacuum-tubes
https://tubeworldexpress.com/
https://www.langrex.co.uk/