This Uncle Mike's holster might fit your need. The holster doesn't come with the mag pouch ready. The seam has to be removed. This was a common mod I learned about on this board many years ago. Inexpensive too!
I've done the same modification as fastjohnson has done. The one drawback I have encountered with it is that the mag base plate can rub against and damage anything you may have on the front of the grip, such as the switch for a Crimson Trace LaserGuard, or a Hogue HandAll Jr. If you don't have those kinds of things on your gun, it works great.
I like the idea... keeps everything together. But since I began practicing a draw from the pocket when I pocket carry. My Pistol is now carried in the right back pocket, magazine in the left front. I can get firearm out of that pocket A LOT easier, and my weak hand can get to and manipulate the spare mag to change as needed. The holster w spare mag on strong side would require moving firearm from strong to weak hand for a reload. Not trying to hi jack the thread but after pocket carrying now for a minute or two, that's my two cents.