Am looking for a photocell that works in reverse, on at sunrise, off at sunset.

 

Photocells (cadmium sulfide cells) all work the same way. They have more resistance when dark than when lit. See if this old thread gives some help - http://forum.allaboutcircuits.com/showthread.php?t=10681

 

As "beenthere" mentions, the photocell is the same, it's the circuit that determnes activation mode.
Dark Activated & Light Activated Switch