We haven't been there for a long time, but I'm fairly sure one could arrange a crane to haul one out, and sort of ad hoc
props---there are builders, highways, and airport
, etc. He'd want to drop the rudder
while he was in the air.
There are flights to Raro from NZ, and what you need to DIY
could be sent to you. I do not have any idea if there is someone there who could do it for your friend; my suspicion is that he'd better get ready to read up on it and do it himself.
Also, if he's from the US, there are rudder makers in FL that I have read about here on CF, perhaps he could have one of them build him one, and ship to Raro. He may wind
up being there longer than he'd like, but it will become a treasured adventure, as time passes. PS. There's a good library.