They were available on all Chargers as code A54, but only in colors GB5, GF7, FJ6, EV2, FC7, and GY3.
http://www.hamtramck-historical.com/images/dealerships/SalesmansPocketGuides/1971/71_Charger_3.jpg

I've seen the Satellite/RR/GTX numbers for rubber bumpers, and they're small, so I would guess the option is probably just as rare on a Charger, especially a 500.