Outer bumper brackets

The 63-65 Valiants and 64-65 Baracudas only have the small suport brackets up front. In back is a bumper cushion that bolts to the rear quarter, behind the bumper outer ends. There is no attachment to the bumper for this cushion. And no hole for a bumper bolt on the outer end of the bumper, as shown on the left side of post #3.
Is there a source for the funky shoulder bolt that holds these to the body, and the captive nuts? For now I plan to use a standard 1/4" bolt with a bushing & a couple of washers