If you are POSITIVE the booster is the problem and nothing else in the brake system....I would have it rebuilt if original to the car. It will help keep the value and the car original.
These were highly recommended to do the proper plating, parts, etc...
https://www.whitepost.com/#welcome
http://boosterdeweyexchange.com/
They are simple to rebuild if you want to do it.
https://www.muskegonbrake.com/category-s/161.htm