AtlLaw - for a j-frame wide spur hammer you would probably have to get ahold of S&W, and I have always found them very helpful, or cruise the Brownells catalog and see if they carry one for a j-frame.
I know there are at least two types of hammers available for the j-frame and the M60 in particular, but my brain has suffered a temporary flatus attack and I can't remember the difference. HTH.