1911 mags are some of the most standard/commonly found mags in use with LE, etc.
You should have no problem finding a kydex holder for them - airsoft 1911 mags are very similar if not the same size as real-steel.
My 1911 mags are WA based and fit my Uncle Mikes holster perfectly.
http://www.unclemikes.com/
Most kydex holsters have screw adjustments for desired tension and fit.