There is a pretty cool set up that allows you to use any spring rate and adjustable ride height (like coil over). Check out this site:
adjustable front springs
the adjusters are made by landrum and AFCO and the springs are standard 5" diameter, 9.5" length springs that are made by several companies (in almost all spring rates). I bought 750 lb/in Hyperco springs and AFCO adjusters from Port City Racing (the whole set up was ~$180).