Anyone know where to get PRR Button Style Marker lights/castings?

Do you mean Class Lights?

 

If P & D Hobby Shop doesn't have them, maybe PSC does.

if you plan to illuminate them, then a slice of 3/32" or 1/8" THICK wall styrene tube with 1.5mm red LED will do just fine. I've done this. it's important to use the thick wall tubing for the proper result. if 3/32" is not available use solid and drill the hole for the LED. I am not aware of a commercially made part.

 

These are 3 mm LED's with no trim. There are smaller LEDs

Bowser Cal Scale also had some parts.
This rear unit light trim is Cal Scale.

Additional picture

Thanks everyone.
Hot water, I don't think these small button markers can be considered class lights as they only show red and are on when the loco is moving in the opposite direction of the lights.
Mike ct thanks for the help I will try this.while a good thought on wagon units, the 3mm LEDs are too big for the button markers.

There were some really small LED's, part of Tomar Industries's passenger car drum lights, and coach lights. If you can detail your marker lights these  LED's, between the red and blue wires,  may fit.