It's come up *cough* as to what I use to carry my spare mags for my 1911.
Well... flashlight holsters. No seriously. I use these.
They're the right size for a 1911 mags and the belt holders can rotate 360 degrees. This makes them very comfortable when they're slung on your belt.
They're also a great length for the magazines, provided you do a mod to the bottom.
As you can see in the attached I sewed some matching material on the bottom to seal the sleeve up.
It's interesting that of my mag holders I don't have any that are stock. And most of them have been modified via sewing in some way.