If you are speaking of the captive washer bolts that retain the rear fascia along the bottom...you would need to got to an auto body supply shop. They are not standard hardware.
Easier to wire wheel, or galss bead them and painted them black. Replacements won't last any longer than the originals. They were either black phosphate or black zinc....cheaply applied to hardware so they don't rust on the way to their application. I have restored many Mopars to concours level... and hardware is one of those little details. In those applications, the correct hardware is often not available and needs to be replated.
Back on topic...wirewheeling, then flat black paint will resemble the original finish and last longer. I already did the hardware on my car.
