Look around for truck body places too. A guy I know here in town works for a place that does flat bed conversions, and those walk-in caps for service trucks, that have a full length door in the back instead of a tailgate.
He says that they have pallets of brand new tailgates, mostly white ones, from everything from 1/4 up to 1 ton trucks in almost every make just sitting around in the upper room at the shop.
They take them off when they do something that replaces the tail gate, or makes it unusable on the new setup, and the truck owners rarely want the tailgates back because they are fleet owners, so these things are usually going to get driven into the ground, and then the junk yard, so they don't want to store 10 tailgates they will never use when they replace the fleet.