Well, I got home early from work today and gave a decent look about for a black recoil system for R4700. Unfortunately, I came up with nothing. . . . . yet.
I'm certain I have at least one black one around somewhere, even if it's just the parts. . . . I just need more time to keep looking.
On your suggestion, the place that did our Black Nitride coating for the R9 Slides and Barrels and other parts, including the recoil system parts was:
H&M Metal Processing 1414 Kenmore Blvd, Akron, Ohio 44314 T (330) 745-3075
I have the regular recoil system in untreated stainless steel form.
You mentioned the round piece worked its way off, do you have all of the parts still or did they get lost?
If you need the inner recoil spring, I believe I have a number of those still around in a plastic bag.
ECR