Same thing happened to my 638. Robar in North Phoenix refinished it in Roguard, nice dark matte finish. Not cheap (they have a couple of cheaper options) but very nice work and a good company--they finished more of the frame than I asked for, and didn't charge for it. Also repainted the front sight better than I had done it.
Especially if you plan on keeping the piece, Robar is a good option.