I ordered them from LKQOnline - a massive parts depot for junkyards. Mine came off a car with 5K on it or something.
Grabbed the calipers for $700. Then bought new pads, stainless steel lines, DOT4 fluid, and slotted rotors. It ended up totaling roughly $1K or so but the braking difference is pretty drastic and now I don't have to worry about brake fade.