Originally Posted by
CV-6
I really don't know what your situation is where you are located, but have you considered replacing the bolt and the nut? I looked at mine and it appears to be an M5 bolt. I test fitted a braze on M5 bolt I use to attach a bottle cage. Fit through the mount and the the brake bridge. It would just be a matter of finding a nut, bolt, and washer at an online store, which should not be hard knowing what size you need.
I have considered different options. Looked from ebay too, but there were only two for sale. Out of my budget, especially the one with both brakes and calibers. Funny thing that the frame had the front Mafac racer brake still there when I got it. Truth is that anything can do of it makes the rear brake sturdy and save to brake, but first I try to find at least the small nut or piece from what the bolt goes through.