There is a company called Karp's Brake service in Upland that specializes in rebuilding cylinders. Their website is http://www.resleeve.com I have used them before. I shipped a power booster off a 65 GMC, they rebuilt it and shipped in back to me in 10 days.
Thanks. I bought a used. rebuilt later model unit from Vista Brake in Vista Ca. Parts are obsolete for the old one.
Vista Brake was VERY helpful. They get a AAA+.