If you are referring to the hinged safety lever in the trigger itself, that's such an important part of the trigger mechanism in terms of safety and reliability, I would consider just changing out the trigger assembly for a new one. They are not that expensive, and it should drop in with zero fitting required.
Smith and Wesson would probably repair it for you at no charge, if you don't mind the wait.
Midwest Gun Works (and various other companies) have MP parts in stock, but I'm not sure if that particular trigger is available.