[Arran]

The easiest thing to do would be to take the control apart and investigate what's going on with that switch, sometimes it's just a matter of the parts slipping out of proper alignment. If the switch is broken it is far easier to find a replacement switch then to replace the entire control, most controls were made by outside companies so it wasn't unusual to find that they use the same power switch in several different makes and models of sets, if you can find out who made it you should be able to find another switch. Ohmite, IRC, Mallory, Centralab, C.C.M, for example, were all used as original controls is dozens of makes and models of radios.
Best Regards
Arran