Horses are sold only by owner accord.  The game does not sell horses, it only auctions them.  If there are no horses here, check the auctions and HA.  In Over Oxer, only your first three create-a-horses are allowed.  At times, you may win a custom horse for services and such.  Barns can be sold here, as well as tack, however, used tack will be sold for 10% less than the original price, and it is not desirable to sell it. E-mail me to submit your horse, etc. for sale.