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

These are available and are excellent sounding EL34's:

https://sophiaelectric.com/products/pages-se-el34

Sounds like maybe I should plan to sell a bunch of KT88 Gold Lions I haven't used in year.

Yes when many output tubes are made in the USSR .

wuhan you can buy tubes on line ebay .  If your tube type is that scarce then maybe look to buy a nice class A amplifier like a Pass Labs , and a nice tube preamp you would be pretty happy .

Here are two reputable tube suppliers that I have used, and have terrific reputations:

Viva Tubes www.vivatubes.com

Brent Jesse www.audiotubes.com

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.