What is currently being made are audio tubes, plus perhaps 6146s,
807s, 811s, 572bs, and a few rectifier tubes. Guitar amplifiers are
why there is still even such a thing as a new small tube business.
12AX7s,ATs, maybe AYs, EL84s,EL34s, 6L6s,6550s, KT88s, and a few
mixafewofem spec beam power pentodes. There are also some power
triodes including 2A3, 300B, etc but at ridiculous prices.

Better you should ask: What tubes can I get cheap in quantity? That I
can get a lifetime supply of cheap? Answer: the tubes that DON"T go
into guitar amps, hi-fi equipment, CB linears (sweep tubes) or the few
specific rare types that are scarce for old radios people collect.
Answer: everything else. Almost all series string heater types. Six
and twelve volt heater tubes for TVs. Design around those rather than
the types you have to bid against guitar and hi-fi people, who often
have too much money.

I would use seven and nine pin miniatures out of the later RCA tube
manuals as much as possible after checking to see that the price is
cheap, from a tube vendor price list. When you rule out popular audio
types and sweep tubes and the rare birds like 6E5 seeing eyes, the
rest are cheap. Audio sharks often buy whole tube caddys and throw the
series string tubes in the dumpster.