As Kevin Kelly pointed out in his book What Technology Wants, most technologies never actually go extinct. There remain people who are still interested in making "new" ones and reparing broken ones. And thanks to the internet, it's fairly easy to find them. For tube radios:

http://www.xtalman.com/ --- Borden Radio Company sells kits to make all kinds of old radios, including tube radios.

https://vacuumtubes.net/ --- "Welcome to the Vacuum Tubes division of Radio Electric Supply, home of the largest supply of New Old Stock vacuum tubes in the world."