First, you will need to determine JB3 or JB5 brakes (if you can't find it on the option sticker, it comes down to width of the front rotor (1.04" front rotor, 2" wide rear shoe is JB3, 1.25" front rotor, 2-3/4" wide rear shoe is JB5).
Quick scan shows that both boosters are still available from Cardone.
Vacuum source is off the intake manifold.
Honestly, unless you're going with a ton of horsepower, good-working OE brakes work fine for most applications, and replacement parts are much easier to find and/or diagnose, and this from a serious "over-braker" (big-brake fiend)