Honestly it would depend on how strong those medical grounds are. If you wanted to look into it further, contact the Federal Office for Road Safety. They are the ones who you need to seek approval from if you are importing a vehicle for reasons of disability.

If you just tried to bring it in via Personal Imports, and rego it in NSW (I'm guessing from Newy in your profile) - it would need to undergo conversion, which wouldn't be that attractive / cheap. Not worth it in my opinion.