You can find a lanyard ring for that 455 here:
Butt Swivel, Original | Gun Parts Corp.
I have bought reproduction lanyards and buried them in the garden for a month. Came out looking very realistic. You can find a reproduction lanyard cord here:
U.S. 1917 Pistol Lanyard braided cord (MISC901)
Nice old war-horse. I have a few, done in 455, re-done in 45 Colt & 45ACP. Might have missed the answer to a question above, but does your cylinder have recessed chambers to fit a 45 Colt? If so, you can also shoot 455 in that gun since the rim is larger than 45 Colt and it will sit above the recess.