Itac makes a quality double magazine holder at a fair price.
I currently have a fobus, but I had to alter it to keep the magazines from falling out. Added velcro strips to inside the holster to tighten it up.
Here is a link to the Itac double mag pouch. Look around you might find it cheaper.
http://www.cheaperthandirt.com/product/2-ITACMP02
Here is another link
http://grabagun.com/itac-dbl-mag-pouch-glk-45.html