ah the wiper arm. surprisingly hard to find considering most people seem to remove and discard it for "weight saving's" or "looks"
removing rear weight actually makes the car more dangerous, as most irish young people would have found out.
I was kindly gifted said wiper arm / motor / hardware i own, by a lad in sydney,
Also of note, the wiring harness for the rear motor assembly is also quite rare.
by sheer dumb luck i have a harness. however all the other bits were placed on the car again
i do wish you luck locating one