I have one used but tested ok high speed Acousto Optic Modulator on Ebay at " http://tinyurl.com/yckuba "
Tested using a Helium Neon laser switching at 1 megahertz (top speed of my fucntion generator) , and optic power meter with scoped output to frequency counter. Aperture at AOM crystal is 1.5 millimeters.
Good luck bidding and see my other auctions while you're looking around.
Rick