Replacement for early small diameter dual diaphragm boosters aren't so easy to find. might be best to send yours to booster Dewey for rebuild. I don't have a link, just read a lot of good feedback on his services.
I sent my Kelsy Hayes booster to him. Besides looking brand new, it works as it's supposed to. Here's his web site: http://www.boosterdeweyexchange.com/
