I have hunted high and low for a FrankenMauser for close to 40 years. I have only seen one up close and personal in all that time and it was obviously ridden hard and put away wet. The fellow wanted IMHO way to much money for it. Still, I haven't seen another.
I saw a World at War documentary showing Axis troops carrying No 1 MkIII rifles they had picked up from fallen Expeditionary troops. There was a rumor that the Germans stripped them of their brass butt plates and replaced them with stamped metal plates. I can't confirm that and have never seen one.
The German's were very willing to use and issue capture weapons on all fronts. Especially to rear echelon troops. The Germans captured all sorts of weapons from France, including Thompson SMGs and issued them to their Artillery troops on the coastal bunkers. We've all seen pics of Axis troops using captured Russian SVT38s and 40s.
As for the Indian troops the Japanese gave British SMLEs to, why not???? They captured thousands of them in Hong Kong and Singapore as well as the other places they over ran during the early stages of WWII from 1930 on. The Indian troops were intimately familiar with the No1 MkIII and didn't require any further training in their use.