I am sure that Napoleon recieved many gifts of firearms. The finest examples of Napoleons guns are to be seen in the Musee de L,Armee, Paris.
Examples of Napoleons guns are to be seen on pages 96 & 184 of the book,"100 Great Guns,"by,Merrill Lindsay.The makers illustrated are Boutet and LePage. The stock on the LePage gun/rifle is similar to that seen on the shotgun picture in the post.The illustrated example has Napoleons crest in gold inleted in the stock.I think that a check with the Museum in Paris would be in your best interest.

Roy Hebbes