Jeff:
At the time, I ordered the parts from Uberti USA (back before the Benelli/Beretta takeover, when Maria Uberti was running the US company.) I had to order the Lanyard Ring pins and rings separately, and in the end they were only able to supply the pins, so I made the rings myself ....
Now, Uberti USA don't seem to offer parts, but I note VTI Gunparts state they are the largest supplier of Uberti parts in the United States. Here is the Remington 1875/1890 schematics and parts list page on their website -
http://www.vtigunparts.com/store/shopdisplayproducts.asp?id=26&cat=Uberti+1875+Outlaw+and+1890+PoliceI note that they seem to only offer the pin (Part UB:155460 at $10 each) or the complete assembly (Part UB:155460/ass at $30 each) but no separate rings ....
EDIT: - Forgot to respond to your question about the serial numbers - on one of my revolvers, the number was stamped on the underside of the frame, at the front, so it wasn't a problem. The other had it in the usual place across the bottom strap of the grip frame, where it would be partially obscured by the lanyard ring pin. I re-stamped it on that revolver. (Legally permitted here in Canada .... not sure about on your side of the Medicine Line ....)