In the Boer War, Sir Sam Steele carried a Mauser C96. Images are available showing him in sam browne equipment carrying the broomhandle, but so far I haven't found a photo good enough to be able to recreate the holster. Afterwards, Sam recommended the broomhandle for NWMP issue. Didn't happen 'though!
It shouldn't be too awfully difficult to make your own pattern. Sheet of paper, pencil, and the pistol. Draw a centerline, place the pistol sights down on the line then roll it down to one side without slipping or repositioning. Trace the pistol and then draw another line 3/4 inch outside the outline of the pistol. Take the resulting tracing and fold along the line and cut out. Voila
Try folding the first pattern around the pistol as a rough check. Modify as you see fit and plan the holster top contour. If you want a military flap, then add it. As this pistol was not general issue there won't be any sealed patterns. Each owner went to a maker and said "make something to carry THIS, and make it sorta match what the other guys are wearing."