The only "pattern" rears I know of are from B&C Express. available only in stock sizes though. 38 and 36 tooth. you can't get seal kits. Brembo ceased making them. Race stuff is servicable, but it has to go to Brembo. Pattern parts in general are very thin on the ground. Levers are available, but most aren't too good. The market for them isn't big enough to warrant them being made.
oh all right, Ive already admitted i dont know what im talking about !!! afraid im a muppet when it comes to the technical mechanical part...my dad would be horrified, he thought it was in our gene pool...