Can’t buy output tubes anywhere except from manufacturers at high prices.

When I lived in a part of L.A. where a good deal of the movie studios were located, I had maybe three or four nearby retail outlets where I could buy the tubes I required to power my stereo. This was especially important during the days of my 8417 equipped Quicksilver Mono Amps which, for whatever reason, regularly ate tubes and spat 'em out. The tube nightmare came to an end, though, when I bought my 6550 powered Primaluna. Ninety percent of the sound. Five percent of the aggravation.

There are plenty of EL34/6CA7s out there from reliable sources.

Viva Tubes and Brent Jesse are the ONLY vendors I bother with.  Excellent service, sales, shipping.  Brent goes out of his way to help even with the utmost, novice, actually stupid questions.   I know....I asked a lot when I acquired a near mint MC-225 built in 1963 a few months ago.

I have a pair of Sophia Royal Princess 300B, special edition, listed on USAudiomart, if that's what you are looking for.

Don at Wathen audiophile may be able to help, he carries Cryotone tubes.