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

All over Amazon, my guitar supply. Depends on the tubes.

At my guitar spply I got quad JJ KT77s Matched Apex from there at a decent price.

Viva Tubes has them. The prices are up but,  the price of everything is up now.. 

Viva Tubes has them. The prices are up but,  the price of everything is up now.. 

They've been out of KT120 and Gold Lion KT88 for a while now. And their supplies may be dwindling on remaining Russian KT88, EH KT90, and KT150. Mullard KT88 are still available for now (up to matched octets), and are excellent. Better get those while you can, if you're in need. I bought a couple octets for my VAC amps.

I just sold two pairs of GL KT88 matched quads on USAM - both quads sold within one day of listing.  I no longer have any amps that run them.  I apparently didn't ask for enough!  So yes, clearly the demand is real and the supply is low.  

@mulveling Have you heard the Mullard KT88 that Viva Tubes is selling, and if so do you feel they are as good as the Gold Lions?