I think the later levels are on Facebook only. You might have to wait a little while for the new levels on iOS. Make sure you always have the latest version of the app installed on your iPad and the levels should automatically update then. I hope this helps :) Thank you!
My iOS app keeps freezing and crashing during the game. I no longer enjoy playing candy crush due to multiple glitches...I have access to the rainbow treasure on my iPhone, but not my iPad.