Disc brake Caliper pins/bolts sizes????? Where to buy???

They're supposed to stick out. On my Challenger there's a little spring clip that sits under the head of pin, between the caliper and the bolt head. Not really sure why its there, but it is.

The pin type brakes only came on E/B bodies, so someone converted the car over at some point. Noting wrong with them, just not original to the A-bodies.