Even though it was designed for Armalite mags, I use this for my MP5 use:
https://www.sealsactiongear.com/cata...?idProduct=428
I can snug in 3 mags per pouch, total of 12 mags if I want to, add in a few more into the long end pouches, the number is very high. Mostly I carry about 8 mags though, easy access, secure, looks cool too.