That was always a popular revolver so a fair number of holsters were made for that frame size. I have Heiser, Myres, Lawrence and other makers' holsters made for the 1917. If they are marked, they usually say something like .45 5 1/2 and also fit the Colt 1917.
Here's one that forum member Wyatt Burp made for me.
This Lawrence flap holster is stamped 45 5 1/2 and it fits the Colt or S&W 1917.
Many holsters that fit a Colt SAA will also fit a 1917.
Regards,
turnerriver