I had a discussion about this with Mark Thomas and , I believe, Alan Sandy some time ago. I had an interest in making a silver mounted rifle, particularly, the John Vogler. I thought, you made one of those for "Sam Everly. Anyway, I had wanted to cast my own, but I discovered that there are all sorts of problems in casting sterling, not to mention that you need at least two pounds of the stuff to cast a set of mounts when you figure in the sprue, risers and such. The recommendation was to make the mounts using sterling silver sheet just like you(I) make iron mounts. I buy silver sheet and wire from Hoover & Strong here in Richmond,VA. Most folks on the East Coast buy from them They will sell you exactly what you need, size and thickness. I would use 1/8" sheet for most of it. You can solder that if you need to build up an area. Using silver solder, you could never tell it wasn't cast. I don't know if you know, but you use different melting temp silver solders to put a piece of silver together starting with the highest temp solder. Hoover & Strong sells all sorts of silver solders that they make. You would catch your waste and filings to send back to Hoover & Strong for re-processing. They will send you a check or send you back mill materials like sheet or wire. I hope that helps.
Mark