I picked up a DeSantis Mini Slide for a Ruger SR9C a few years back...I use it for the Shield 9 & 45, the 3913 and the 6906. A little twist of the retention screw dials it in. It also fits my Kahr CM45, but I seldom take that out.
I also have a G&G IWB for a Glock 27.... works just fine for all of the above also.
I have a few individually-fitted holsters, but I tend to use the one or two that fit everything the most. I guess I'm too lazy to go in the holster box to find the "special" ones.