Your Excella should have 12" brakes. You can get them at any trailer parts/repair place, such as Redneck trailers, or any RV dealer. They are not Airstream-specific. They can be gotten loaded (contains everything, including the magnet), for as low as $50 each. Left and right are different, so pay attention when installing.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.