xray, photomultiplier and laser tubes are still SOTA. PM tubes in particular have a huge number of glass feed through for the intermediate plate voltages.

They are also made in China. There is also one American company that makes a single audio tube, the 300b. They bought the Western Electric tooling, materials, and trade dress from whoever had bought it from AT&T.

I’m not sure where non audio vacuum tubes are made. I’m sure there’s a variety of companies around the world making X-ray, transmitter, laser, etc. tubes.

A lot of the demand is from guitar amps, while you can just as well simulate the behaviour of a valve amp these days there's still plenty of demand for the real deal. As long as the likes of Fender, Marshall and so on want to supply valve amps to the mass market there'll probably be factories producing ECC83s, EL34s and the other common audio valves. In a lot of ways the combination of electric guitar + valve amp basically is the instrument in some styles.

There's also a niche HiFi market, my daily driver audio amp is a 1960s Leak EL84 amp. It's a cool bit of living history and it's very non-fatiguing to listen to for long periods.