Ray,
I don't know about the Key Company that you mentioned. But we have some pretty good handy dandy people on this forum who are capable of making pretty good reproductions of just about anything. (Hugh is a good example). There was another guy here a long time ago, who made a stock/holster for the 1900-06 American Eagle that looked pretty darn good in his pictures. These people may make these things, on their own, without any government approval. Accomplished, yes. Legal, I don't know.
It is hard for me to imagine that an artillery stock like this was made in 1913. Erfurt started designing the artillery in 1911, proposed it in 1913 and didn't let out a contract until 1914. That didn't leave a lot of time for someone to design and manufacture a holster/stock for the artillery. Just my ramblings.
Just more ramblings. I got 1600 posts now. Isn't that the address of the White House in Washington DC? I wonder if I can get President Bush to treat me to a base ball game with some hot dogs and some beer as a reward. I just hope that it isn't between the Detroit Tigers and the Texas Rangers. I might end up paying for everything out of my pocket.
Big Norm