Hi Mark,
I recently went through this, using Gary's excellent thread, to repair a couple of old sunvisors that were in really bad shape.
The sheet metal piece that is spot welded to the bar frame was torn and only barely holding on to the bar frame. I separated it and flattened it out, and got what you see in the first picture below (as you can see, a piece was missing altogether). I used that as a template to cut a piece of sheet metal the same size. I used a drill to get the holes in the right places. Then I bent the sheet around a metal rod of the same diameter as the hinge, to give the right final shape. Finally, I brazed this onto the bar frame in the right location as shown in the next two pictures. The job was not beautiful---I'm a real amateur at brazing, but it doesn't matter because it's hidden.
In the case of one sunvisor, the speed nut was entirely gone. I don't think you'll manage to find those particular speed nuts, if one of yours is lost or broken. I looked around and the closest I could find, at Home Depot, is in the first picture below. If you use this, you should grind the tip of the screw so it's not so sharp. The original speed nut has a second fold to protect the interior of the sunvisor from the sharp tip of the screw. The second picture shows the speed nut clipped onto the sheet metal. On the other side (third picture), I used JBWeld to glue a washer for the screw to bear up against, because the original speed nut includes that as well.
Hope this helps, or gives you ideas for doing a better job than I did. My approach did work and is not visible when the sunvisor is complete.