Fair enough. Just curious.
Best place to start would be to call S&W themselves.
If you're lucky, they'll have the part in stock.
If not, numerich or midway might have one.
Should be about $175 at the most if I remember right.
Either way, if they do have it or you have to source it yourself it still needs fitted. That requires a trip to S&W, might as well have a trigger job done at the same time. Have them do a master action tune on it and have a very nice custom revolver with an intact factory warranty.
Not that I've put any thought into a similar project before...