I have a shoulder rig made by Passport. I believe mine is the sidewinder. I got it just to try out and it works fine (not as comfortable as a better made one I assume), I'll replace it with something better one day.
Passport Shoulder Systems
I have one for sale in the items for sale section here.
The shoulder holster I use for my Kahr is a mixture of Galco system parts. I use a black Miami Classic harness (because I usually wear black tee shirts), a Classic Lite holster because it is thinner than the rigid leather (nicer) holsters, and an ammo carrier for a Walther PPK/S becaise I already had that and the magazines fit. This shoulder holster won't win any beauty contests, but it provides comfortable concealment for long periods. I even wear this under polo shirts.