I am dealing with this same issue and unfortunately, my original fastener is long gone. They do not sell replacements that I can find. After some quick measurements, a 5/16" x 7/16" long shoulder bolt will do just fine. Add a 1/4 -20 nylon lock nut on the other end. Should be plenty of room. Eliminates the push nut. I had to order the bolt from Mcmaster Carr and about the same price as a 5/16" pin with a push nut.
If you have a good hardware store nearby, you might be able to find the pin. Push nuts are easy enough, it is the pin that could be difficult.