The body of the holster looks very much like those manufactured for use with the 9-mm Dreyse by the Imperial Landgendarmerie. Examples of these are shown on p. 188 of HWIS and in the thread
http://forum.lugerforum.com/showthread.php?t=21274. The flap is quite different and may have been a replacement as suggested by Norm. It apparently does not have the
L.G. stamp found on the former Landgendarmerie holsters but I would not expect it on a holster manufactured in 1939.