How do I find the valves on a toilet with hidden pipes?
I believe that your statement "the toilet is also supposed to apparently have a shut off valve" refers to rough plumbing and NOT the toilet. I am not aware of any toilet with a shut-off valve inside the toilet. If you don't have an external shut-off valve close to the external supply hose/pipe that connects to the toilet tank, you may not have a valve. In this case, the only way to turn off the water supply for the toilet is to find another valve on this system- most likely the whole-house valve, like keshlam suggested. It is unlikely that the shut-off valve is in the wall.

This image is a good example of a toilet shut-off- valve: