power brake booster

You can get a replacement booster at any auto parts store.
A lot of people would like to know where those stores are.

Many people recommend Booster Dewey (google search), but not cheap.
Don't pay too much since a guy on ebay now sells a GM type booster w/ Mopar brackets & rod for ~$150. See posts here.
I put a junkyard booster/MC from a 98 Breeze on Dart brackets, which is the ultra-cheap option. Real easy to get parts now.