I bought a Black hawk serpa concealment holster, right hand matte finish for my Ruger SR40. While I have not had it very long, I can say that I am happy with it thus far and its comfortable enough for extended wearings.
One common issue that makes it hard for many to find holsters for the SR40 is that the vast majority of holsters and their labels on the box/packaging say only SR9. But the black hawk holster I got in size 41 fits the SR40 perfectly. As an added bonus it also fits the wife's SR9C tight as well.
Hope this posting helps members out and makes the search for a holster for the SR40 easier