when did apple stop selling iPad Air 2 16GB

A little while, ago.

Apple had acknowledged that a 16 GB iDevice, simply did not have enough usable storage space.

So, iDevices now come with a baseline storage of 32 GBs, now!

No more 16 GBs iDevices any longer.

Check out Bestbuy. A while ago they had Air2 16GB for $350. The ones I saw were all on IOS 8.

think all the complaints about only 12GB being avaible for data and apps made apple stopped making 16GB ios devices