Sources for Used Equipment

If ControlBooth's Classified Ads area doesn't have exactly what you are seeking...

Of course there's the phenomenon known as eBay, and in some larger cities, Craig'sList may be viable. Also, save shipping costs by checking with your friendly local vendors, see Best Dealers for Supplies & Equipment, as many, especially those with a Rental Dept. will rotate their stock and sell old or un-rentable items. Other sites, specific to the entertainment industry, are:

UsedLighting.com - Buy, Sell, & Trade Used Stage Lighting & Theatrical Lighting Equipment, a division of 4Wall
Stage Equipment, Lighting, Audio, and Video, GearSource
LED Source, LLC, all things LED
Stage Lighting - Used Lighting, Used Audio, Used Video - Solaris, Solaris Network
Soundbroker- Used Entertainment Production Equipment, SoundBroker
LightBroker, (no relation to above) the sales arm of T2K in L.A.
AVForSale - Audio Visual / Entertainment Equipment Liquidators, by CB member Oldschool
PSW Sound Reinforcement Forums: LAB Marketplace
Earl Girls Used Gear, Lighting, Trenton, NJ

Although Production Resource Group, PRG : Used Equipment, does not maintain a website (one must email the appropriate department), the company bills itself as having "the world’s largest inventory of used lighting, audio, and video equipment for sale."

Disclaimer: The listing of the companies above is for informational purposes only, and is in no way an endorsement of said companies by ControlBooth or any of its members.