I've seen MANY tang safeties on Mauser sporters in Germany! I believe these were made and installed by individual gunsmiths when they built sporting rifles from military actions. I know of no such gadgets being made for instalation, but suspect if you contact New England Custom Guns they could tell you if such an item is available, or who could make you one.
Both Mauser and Voere made post-war commercial 98's using a tang safety. The Mauser version also kept the bolt safety, the Voere didn't. The Mauser version used a Timney trigger and was contected with a paper clip to the safety, much like MkI Rugers. The Voere was a self-contained one piece unit. In each case the safey merely locked the trigger.
The best way is to install the sliding type that blocks movement of the sear, using an original Mauser trigger assembly. I believe Recknagel makes them and NECG can get them for you.
The stock work required. Unless the safety is part of the receiver tang, as on the Ruger Mk I, you will have to inlet the wrist of the stock. Difficult for amateurs to do nicely, an added expense with the pros.