Discontinued from Ford, but was also used on 71/Pinto, Maverick, and 78-79 full-size Bronco. If you are OK with used ones I would check with Don (OMS) or Mike @ Motor City Mustang to see if they have any used ones looking for a new home. If you do score some used ones, check them carefully, there was a problem with some of them breaking on some early models.
To my knowledge, there are no repos for this bolt. I have tried several times on the AMK site and have not found a replacement. There is a site I have used before that shows stock on some NOS (D1ZZ-6560392-A) but you will have to contact them for quantity and pricing info.