Some King Arms mid-cap (95 rounds) G36 magazines just arrived at So Go. You should talk to Jon about them.
I think M16/M4 mags will probably be cheaper than comparable G36 mags. Everyone and their dog, myself included, has a M16/M4 series rifle or a rifle capable of using M16/M4 magazines. There are so many of these rifles that their magazines are probably the most common ones in play. As a result, the marketplace keeps their prices lower than for other sorts of magazines.
As a sidenote, there are G36 adapters that allow G36 weapon systems to use M16/M4 magazines. They're reasonably priced (usually under $ 40.00) and easy to install. So Go can probably order one for you. That way, you can still use your G36 but with the cheaper M16/M4 magazines.