For a repro holster try
http://www.northridgeinc.com click on parts in the left panel then Luger, but they are belt types. In John Walters book, the Luger Story, ppg 140-141 he states essentially that the pistol lange, or what we call the artillery model was to be issued with a sholder holster to non-commissioned officers and mounted men of the infantry and artillery munitions columns who have previously carried revolvers are to be armed with the lange Pistol 08. There is also an indication that it was intended to be issued to airmen and field artillery, and to equip fortifications. A good book at a reasonable price for your library.