The original finish was zinc plated, it might have been bright zinc plate or BZP as it’s known but all the ones I’ve ever seen were kinda dull so maybe not. They ain’t easy to find, either NOS or undamaged but do turn up occasionally on Ebay. I have a couple of the D rings around as one of the members had some made in Europe and I took the chance to stock up on them. The other should be easy to find, just do a search on Ebay for a nitrile ring with those dimensions.