The mirror on your door was not the tri pod type but they are very common, there are 3 different tri pod lengths of the arms that mount to the door. I suggested the single arm one because you already have it on the driver side and have the holes on the passanger side, the inside mounting flange i believe is reproduced but you may find one laying inside your door bottom unless its stuck in place where the mirror mounts by rust?
Tell Wes what you have is a single arm with a 3 bolt hole flange on the door, i would take a picture of the driver side one and email it to him, he has his email addy on his webpage.
http://www.classicheartbeat.com/
Per the other stuff, salvage yards or here on the parts board.