No theoretical reason why r couldn't be done, I think the more common guitar amp tubes are even in commercial production in China (and supposedly they've improved the robustness too). Bit of a niche market though.

glasslinger on YouTube has been experimenting with making some of the more unusual tubes too: https://youtu.be/BXAjspPLzRQ

Uh, what?

Production involves pumping down to high vacuum, heating to degas, and then refilling with neon/argon at low pressure. Granted the production tube isn't at high vacuum, but it's not equivalent to ambient.

When they fill it with gas, wouldn't you say it is no longer a vacuum?

This entire class of technology was universally known as "vacuum tubes" for a good reason.

Why do you say there's no vacuum? That's one of the steps in the videos.

Technically, at the end of the process, the resulting tube's gas pressure is high enough to be called "low pressure" rather than, say, "rough", "medium", or "high vacuum".