Several years ago, I had a Browning Buckmark that I used for rimfire practice. Like the Ruger 22/45, its grip angle and safety placement mimicked a 1911 quite well. I had a nice "pancake" style holster made for it by "K Holsters". www.kholsters.com
By the way, if your Ruger is the bull-barrelled model, with the undercut "gut-hook" front sight, Millet makes a nice ramped replacement sight.