A "Flash Chromed" S&W K-frame hammer is what you are looking for.
Some of the early production 66-4's were equipped with them.
Your best bet is Brownells or Numrichs - or placing a WTB ad on the S&W forum. Good luck! Regards 18DAI
S&W Model 19 Combat Magnum. Everything you need in a revolver, and nothing you don't.