There are millions of original, NOS valves available at reasonable prices. When transistor radios came in every radio shop was stuck with thousands of valves and they never go bad. They are made of glass and the inside is under a vacuum so they will last for 100 years or more in dry storage.
A friend of mine has 25000 of them in his basement. All gathered up from defunct radio repair shops within a radius of 50 miles.
They are all substantially the same. By that I mean a 6AV6 is a 6AV6 no matter who makes it. The old ones are usually superior to new Chinese made valves. Russian valves are sometimes very good, sometimes not so good.
The best valves are old Mil Spec (military specification) army surplus. They were made to a higher standard than ordinary valves.
The valves themselves are not usually the problem. A tech with the right tester can test them and tell at once if they are up to spec or not.
The most common fault in old car radios, is the vibrator. It changes DC to AC. Sometimes they can be repaired, or a NOS replacement secured. It is also possible to make an all electronic substitute which lasts much longer and has the additional benefit of eliminating the hum.
Next up is the capacitors. The old ones were made of wax paper tinfoil cardboard and wax. They had an average life span of 10 to 20 years. They can be replaced with modern Mylar capacitors which have a much longer life.
A good valve radio tech can bring your radio back to life and make it work like new. In fact much better than any new AM radio. It is also possible to add an FM receiver, or MP3 player to play through the original tube amp circuit.
Here is a supplier in Canada who can furnish a copy of the original schematic as well as capacitors. I have dealt with him before and found him reliable.
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