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

FYI: B&H sells "Telefunken" tubes but they are not German made Telefunken tubes.

I asked TELEFUNKEN Elektroakustik and they told me the tubes were made in partnership with JJ Factory of Slovakia.

I thought it was always common knowledge the "Telefunken Black Label" tubes were just JJ’s. Always look at the shape of the glass dome (especially on EL34, for example) -- only JJ’s have that goofy, awkward rounded dome shape.

We at eastendhifi I have KR Audio tubes in stock. We carry the KT88’s, the 300B tubes, as well as a 300 BXLS from KR Audio.  Yes, they are certainly not inexpensive, but they will sound better than anything out there, other than maybe Western electric, and they will last longer than the JJ tubes. you can check out what we have available at eastendhifi.com.