Inside of fixture:

Hold the sensor body and unscrew the plastic ring nut.

Mark the wires (or mark on a picture of the wiring) what everything is hooked to (this one loooks pretty simple though).

Even a big box store should have the sensor.
If they do not an electrical supply house WILL have the sensor.
Take the old one with you, though they are pretty 'standard.'

Hook everything back up, turn on the power.

The one you have looks like a three wire unit (I can barely see a white that looks like it comes from the sensor).

Black is power in, red is controlled power out.

White goes to all the the whites (should be a white from power in, a white from each socket, and the sensor - make sure you use a large enough wire nut for the four wires).

Both lights have to hook to the red to be controlled (and the white in the box of course).

Red to black on the lights (or the bottom button on the bulb socket).