You can buy them new from Ford, with brackets and brake pads, under part numbers 3R3Z 2B120 CA, and 3R3Z 2B121 CA. Pretty decent pricing on them, last time I checked. You should do a bit of grinding on either the spindles or the caliper brackets, to give you full range of movement once the pads start wearing, and the calipers move on the sliders. Try a search on the topic here, and on TCCoA. There have been some in-depth discussions on the installation process.
Paul, the pads are unique to 99 - 04 Mustang V6 & GT. They clamp on a large area of the rotor surface, one of the benefits of this upgrade.
cheers
Ed N.