Anders, i contacted TheRamman on ebay about his brake booster rebuild kits, and brake parts. Specifically the mopar A body one from 1973 - 1976. This is a Midland Ross type unit with the strap holding the halves of the booster together. He told me a rebuild kit for this booster would cost me $145, he just doesnt have it listed on evilbay. So yes the kit to rebuild this is out there. I mentioned to him about putting this kit on ebay.
I took mine apart, and yesterday i dropped the steel parts in a water and molasses mixture to remove the minor rust on everything Just checked it today. Everythings looking good. Almost all cleaned up. Some minor pitting from where dot 3 brake fluid caused a bit of corrosion from a leaky master cylinder. I plan to sand this smooth, and may just have the canister halves powdercoated black. This solves any rust issues inside the unit. I would have painted it , and coated the inside with the epoxy primer if it was pitted badly , but the metal is really nice and for the most part smooth and will take the powdercoat nicely.
Hope this helps
Matt