Do you mean a four wheel trailer that the front two wheels steer? Are you familiar with the tractorhouse.com website? I hear of hay barns where they load the wagons and have kind of drive through hay barns so they can be unloladed later when the dew has come down. Backing up a trailer of this type can be frustrating using the drawbar. I may not be current but you buy them new and they fit into the bed of a pickup. You buy the wheels separately. I know I looked at them at a central tractor place once. I kind of sort of think they morphed into tractor supply. They should be cheap used as kicker baler wagons or round bales and hay spears seem more common lately. Not sure if the big square bales and wagons for them play into the picture or not.