Goto LA Police Gear. They have everything known to man as far as pouches, mag holders, belts, harnesses, armor plate carriers etc. Everything the "Tactically Correct " person needs and then some.
If you look at Voodoo Tactical and Condor you will find they make one two and three mag holders as well as double version that hold two, four ,and six AR/ Mini14 style mags. These come in about 3-4 different styles of hold downs, attachments, and various colors.
They can all be adjusted to carry 10, 20 and 30 round mags and are not that expensive <$20 for any of them.
Here is one I have Voodoo Tactical M4/M16 Double Mag Pouch
and I also have a three hole one too. IE 4 mags and 6 mags.
Also look at Condor stuff here: Results for Condor mag pouches - LA Police Gear
They also have single hole and triple hole versions of this same one. You will have to look around a little on their site to find everything.
They have everything known to man at this outfit. The Voodoo and Condor stuff is very inexpensive as opposed to the bigger brands such as Maxpedition and I personally can't see a bit of difference. Not much in a name when it comes to this type of equipment. All of it is made in China and probably at the same factory.
You should be able to find something that will work for you here. If you can't,,, go back and look again. it doesn't get any better than LAPG.