They, like most parts, were available over the counter.
If a car has M05 on the broadcast sheet, they would have been installed at the plant.
Barry:
I believe they were part of A05 (Body Protection Group) also.
A05 was Vinyl Insert Body Side Mouldings, Door-Edge Protectors, and Bumber Guards, Front and Rear with Rubber Insert
My '70 R/T convertible has A05 on the fender tag, and a PO told me he removed them along with the side mouldings in the '80s when he did a re-paint.
I have the mouldings and guards, but I need the edge guards also. I saw a set on ebay last year and should have grabbed them! {:<(
