Depending on what kind of money you are looking to spend, there are several ways you can go.
Disc set-ups from a `73 and newer a-body is one way to go. If you can find a doner car, take the calipers, spindles, and lower control arms, along with the master cylinder and propositioning valve. It is a bolt-on affair.
If you are willing to spend $800-1500, you could go with one of the aftermarket set-ups, such as Wilwood or MP Brakes.