Can you post a closeup of the broken shaft?
I have to wonder if there isn't a similar VHF ham rig that Icom made... some of those can be had cheap enough to use for parts. If there's enough shaft left. maybe you could solder on a short length of brass tubing - though you'd stand a very good chance of melting the guts of the volume pot. With enough luck and skill you might be able to drill and solder or epoxy in a shaft. Or maybe it's a common part that's still available from electronic parts suppliers.
Tough to say without seeing it.
