Outside mirror

I am going to start using my 66 Dart GT as a tow vehicle for our small camper trailer. Rear vision will be impaired somewhat when towing and given that I live in New Zealand and we drive on the left side of the road I wanted to fit an outside mirror to the right hand door. I have managed to pick up a mirror from an Austrailian right hand drive Valiant but I was wondering how common the extra right hand side mirror was originally. I have Googled pictures of Darts and it seems very few cars are fitted with the mirror on the right side.