Using 90's VW Jetta rear view mirror.
Not sure if this is already known but I found out today that a 90's VW Jetta rear view mirror will fit the e30 mounting stalk. It's the right size to fit the ball. A tug will pull the jetta mirror off its mount but you will have to remove the spring clip to install. I installed mine without the spring clip for now but will install it this weekend. I will have to remove the mount to install the spring clip. It looks like it may be a little challenge because you will have spead the clip to slide it over the fingers. Another option that may work is to keep the spring clip on and place the mirror on a hard flat serface while trying to press in the e30 removed mount. I havnt tried it yet so I can't say for sure. A Jetta mirror may be easier to find in an auto salvage yard.