Check over on the S&W forum. There's a guy that goes by the name of shooboy, that makes them, and some mighty fine gunsmith hammers. He does a land office business. I've got one of his hammers, and his work is beautiful. He makes several styles of both the hammers, and props. he'll install a cartridge base in what ever caliber you want, on the props.
i got about ten of them, got them from my dealer who got them from his ruger rep. before getting these, i had planned on making some like the one shown in flatgates picture. would be easy to make. you can get the medallions from ruger.