Is your gun already drilled for a lanyard ring, or not? If not, then you'll need a machinist to make one or two holes in the grip butt depending upon what style lanyard ring you use. Here's a photo of a S&W .455 from World War I that I had to get a lanyard ring for. It had the lanyard ring removed, but was originally drilled for one. The edge of the hole is rebated so the stud has a collar to pivot within - very nicely machined work they did back then.
I don't know how they were installed on 1917 Colts. On Webleys, there was a simple threaded hole and the loop stud screwed in, and it wasn't secured. On S&Ws, the .455s, 1917s, and later Victory guns, the method was a smooth-bored hole, and a cross-pin to retain it. The lanyard stud is smooth sided, not threaded, and it can pivot within the grip frame. It is grooved on the side to catch a retaining cross-pin. Here is that style with the lanyard out of it:
In this photo, you can see the cross-pin hole just below the grip stud.
I bought a lanyard loop at a gun show for about $12 or $15, then a blued roll pin at Ace Hardware. Besides a gun show, they show up periodically on Ebay and Gunbroker. I do not know of anybody making reproductions - the market is pretty small for that. S&W is currently making a reproduction of the 1917 and it comes with a lanyard ring. You might call them to see if that part is available separately.