I don't see anything there relating to Vienna or Ferlach. As for a buttplate, this gun would undoubtedly be shod with a horn butt plate and you can probably find one large enough to fit it yourself. Probably need to plug old screw holes in butt and re-drill. Galazan may have some horn butts or just look around at a larger gun show. These plates typically had a few lines of horizonal grooves across the center of the plate with both the toe and heel smooth. If you get a blank it isn't hard to fit it and file in the grooves.