I would first check with a local dealer and see what they can do for you. Many trailer parts are interchangeable between brands, depending on the item. A good dealer with a good parts department can do wonders. If they absolutely have no leads, then start checking RV salvage yards. A simple internet search (RV Salvage - Your State), and you'll probably find something.
If both of those fail, then you do have the 3rd option as pigman1 suggested, attempt to have one custom made. (myself??? if it were me, this is the order of events I would take.)