Unless they are massively large MP5 pouches, the mags will not fit. I tried putting a MP7 mag into a MP5 pouche and it would not fit for love nor money. I ended up taking p90 mag pouches and cutting part of the bottom off so it would not fall in to far.
There is this too:
http://www.mayflower-rc.org/store/index.php?c=0&p=66