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Moflon Slip Rings (MC330; 18 leads; $65 - www.moflon.com)
They also make fiber optic commutators that look like they should work well for integrated optogenetic setups: http://www.moflon.com/mfo.html
It would also be pretty easy to mount 1-4 LEDs below the commutator and just route the LED drive currents through the slip rings, this could be easier in more demanding applications.