Antique light fixtures are popular due to the current interest in architectural salvage. You can find businesses that deal in vintage or antique lighting fixtures in your area or online by searching for that term. Many towns have shops that deal in architectural salvage so look around in your area. The amount you get for a sale will depend on the condition of the equipment. If there is a lot of damage or deterioration, a dealer will have to figure the cost of restoration (as well as overhead and profit) into the amount he is willing to pay you.
Of course, you can always try Craigslist. Selling on eBay may prove difficult due to shipping costs.