power brake booster

If you need more vacuum than your cam provides, you can install an electric vacuum pump. After-market ones cost ~$300. Recent diesel cars (VW, Audi, ...) use them and are ~$50 used, but you need to wire a vacuum switch ~$30. Another option is a non-vacuum booster, using your power steering fluid (if you have), termed "hydro-boost". Those are much smaller than a vac booster.