How to track down control/switch for light fixture
Once you've tried the answer in the comment:
Get an edison screw outlet adapter (basically the bottom half a lightbulb with a socket at the end).
Get an electrical tracer, and attach the leads to some wires poking out of the socket (this just makes it easier -- you could also take the socket down and attach to the wires in the ceiling).  Now wave the wand around and trace the wire.  It should go to a junction box or a switch.