Interesting problem. I would think that you might be able to see how the passenger side mirror is mounted by looking up underneath on the outside. If it's attached to a mount of some kind that's attached to the frame, it might be fairly difficult to find one for the drivers side. But it could be symmetrical (if the mirror isn't attached directly to the frame through the end cap), which could possibly fit on the drivers side after rotation.
In all the years I've been perusing the RV forums I don't think I've heard of anyone doing this. You are a trailblazer, Poppy.
I'll keep my fingers crossed for you.