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Quite possibly because S&W makes so many models that have their own hammer shroud (Models 638/649), or are hammerless (Models 442/642 with an internal hammer), that they figure there's no big market for a factory add-on shroud for the Models 36/37/60. Probably the same with aftermarket manufacturers. There is also the vintage Bianchi Lightning Hammer Shroud grips (made for them by Pachmayr), that turn up occasionally on the auction sites. Their drawbacks are that they are a bit large and cumbersome to use.