Try Jack First in Rapid City, SD. Google them for contact details.
What is the problem that you think a new yoke screw is going to cure? Does the yoke bind when swinging it open? The earlier 3-screw sideplate guns have 2 round-head screws & 1 flat-top, I usually "fit" both of the round-toppers to work in the forward hole by filing them slightly shorter as required to eliminate any binding on the yoke shaft. Doesn't usually take too much. I can't think of any oher problem that might be screw-related.
Extractor rod starting to come unscrewed, maybe? Did the gunsmith look your gun over yet to ascertain the problem?
Hah. I was just about to leap head-long into this thread with some brilliant words of wisdom, until I saw the term "Yoke pin". I have no idea what that is, so I'll go back to my corner, and keep quiet.
We're not talking about the old yoke detent pins from the 1910's through 1920's, are we? Nah. Couldn't be.
Exactly. It must be fixable, they got it in there in the first placeYikes! Are you saying that the yoke stud (the part that slides into the frame, came loose from the yoke body (the blued part that shows)? If that's the case, I've never heard of that happening, so I have no advice to offer (good, bad, or other). I wonder if that's even fixable.