A very talented machinist friend made a pair of brackets that are designed to attach to the lower front corners of the frame inside each of the Honda fabric upper doors. His brackets allow mounting of the Honda mirrors.
He is not interested in making more brackets so I can't share his name and contact information. I encouraged him to patent his products and sell them commercially but he has a career, wife with a career, young children, and varied interests and is not interested. I'll share a photo hoping he doesn't mind me giving away his intellectual property.
The photo shows the tube frame inside the left Honda upper door with the fabric unzipped and partially removed from the frame. The mirror bracket is attached in the lower front corner of the frame. The photo depicts his original prototype before he predrilled the holes that attach the mirror screws.