There are lots of folks who make custom grips for Blackhawks. Any that make them to the customers grip frame could do these near as easily as to a standard frame. Gent I had do most of mine I always sent the grip frames to for a perfect fit, but he is long retired, maybe passed on by now.
Simply do a search, find those that either "require" the grip frame or will build from one, if they want your business remove the frame from the revolver and send it to them.