Scota: that part, in the original is not a casting but a formed piece of what looks to me like coin silver. It is not a difficult part to make: cut a cavity the shape of the end of your buttstock in the end grain of a piece of hard maple, and a forming plug that is 1/16" smaller all over. Anneal a piece of coin silver, german silver, or pure/sterling silver cut to size, and squeeze it between the two pieces of wood. Trim the edges and the tang up the back, and BYU.