E-Bay.
At least twice a week I bid on a winch, still have not "won" one. You need to specify the make in your search or you will get literally hundreds because of all the trailer and Jeep winches. My searchs are always "winch make" where "make" is Lewmar, Harken, Barient, Barlow, Andersen, etc. One at a time.A couple of other sources are Surplus Unlimited(Link below) and Sailor's Exchange: http://www.sailors-exchange.com/