How to manually change orientation of iPad
Seems like you have issue with the gyroscope inside the iPad. He's the one detecting when the iPad is turned.

Your better chance would be to go to an Apple Store if it's still under guaranty, maybe they'll find a problem and change it for you.

To answer your question, no, there's no hardware button to change the orientation. But you can lock it, and here's the 2 possibilities. If under Settings • General • Use Side Switch to


Lock Rotation
Just flip the switch over the volume button to lock the iPad in it's current orientation.
Mute
Double-click the Home button, slide the apps to the right and click the button to the further left. It will lock the orientation.