What part of the switch is broken? If it is not the slider, then maybe you could mix and match parts with one that has an Alps-compatible slider. Apple Extended Keyboard II (AEKII) - in a variant that was made in Japan - has that type of switch. AEKII's with other switches are more common.
I think all Amigas - from the Amiga 1000 up to the 4000T and CD32 - used the same serial protocol, only different connectors. So you should at least be able to connect a different Amiga keyboard to it with an adapter.
(The only exceptions were the 1200 and 600 that had a ribbon cable to the motherboard, but still had serial communication between components on the motherboard, if I'm not mistaken.)