g36 specific pouches are available at ehobbyasia flyye single g36 mag pouch and tactical tailor g36 mag pouch... 20-30-33$ each, you will need 3... which will allow you to carry 6 mags +1 in the gun.
http://shop.ehobbyasia.com/catalogse...g36+pouch&cat=
They are indeed a bit expensive, but if you want to keep the mags, you will have to pay the price. Those pouches are made specifically for the larger g36 mags, and you don't have to compromise with double ak pouches or triple m4 pouches.
Your other option is using magpul g36 pmags, they fit in m14 mag pouches, or very tightly into m4 mag pouches.