Give S&W a call, but would not surprise me that the blacken parts are already SS instead.
Hence if SS and just blackened,  could just bead blast the blacken steel parts with 400 glass bead at about 40lbs to remove the blacking, to get them to match the sheen of the frame instead.

If they are not just coated SS parts, then they may carry the parts in SS that are already sheen matched instead.

As for someone else beaver tail, most would require the frame tail to be radus, as well as blending of the frame to bevertail as well.