Brake Whoas

I think I found my problem. I pulled the booster apart and found a small split in the acordion rubber boot . When the boot streaches the split opens up and lets the vacuum escape. The problem now is trying to find a rebuilt on. Cardone is the vendor for all the local name parts houses and they have none in stock. Does anyone know where to get a rebuild kit or a rebuilt one? Acually this is a 73 Dart booster.