http://www.hpiracing.com/products/en/6746/
Purple super firm hpi springs may be a little longer so might not have to preload as much. Take the part number to your lhs and see if they can order or you can order it online.
http://www.hpiracing.com/products/en/6745/
Next step down if you dont want the super firm these are thier firm springs and should still help out.