the 110rd magazine already exists for a previously made rifle and the GSG 16 uses the same magazine system.... The GSG 15 is a different magazine system and only the standard 22rd magazine are in circulation for those and the ISSK and Anchutz versions of the same.
Sadly you will have to buy another 22lr rifle to get 110rd capacity....given how reliable my GSG 15 has been I didn't think twice about ordering the 16 given that its a good buy with lots of features.