To find a holster look for something made for the 39, 439, 639, 59, 459/659 models. Those are the 1st and 2nd generation S&W 9mm. Any holster for one will fit the other. Some of the 3rd generation S&W 9mm holsters will also work but you'll need to check those. Some 3rd gen S&Ws had large trigger guards and others had small trigger guards. Their trigger guards will also be squared. Depending on the holster design something for the 3rd gen might work.
from: http://www.thehighroad.org/showthread.php?t=231662