Actually, they are likely just automotive caliper put to use for trailers..... Take one off and take it to an auto parts store. They should be able to cross-reference the casting numbers to come up with a replacement new or remanufactured unit.
I think that I would be more likely to try a privately owned store that was associated with a national buying like CarQuest or Pronto than an AutoZone or WesternAuto; people who own their store and work in them are usually more knowledgable about such things than kids hired to work the counter in a chain. (No disrespect ment to chains - I buy most of my parts at them!)
