I had the same caliper problem, got a decent used one from an eBay seller.
My other (corrosion based) gripe is that the nuts / studs on the exhaust pipe collars have rusted away, so maybe worth taking a look at those before they become a problem. Managed to fix one side, new (original) studs and stainless nuts, but getting to the other side will be a real bugger of a job, so leaving it until it really needs dealing with. I got a complete (new) exhaust system, again from eBay - £80, ready to go on the bike at some point, so the old header pipes could be cut off if necessary.
Coated engines cases are a daft idea, prior to the Scrambler I had a T309 Trident. The black coating came off the engine cases in large chunks.