Has the hinge pin actually been lost or is it still in place? Hopefully, the other parts once retained by the missing pins have not been lost. You should send it to a talented gunsmith who won't attempt to make a million dollar project out of it. My choice for someone who will not nickel and dime you to death, and will tell the truth about what actually needs to be done is Keith Kearcher in Bend, Oregon. Not only can he make new pins and clean and reassemble the gun if the parts are there, he is a barrel expert who can evaluate your gun for safe shooting.