if your ok with bending the truth a little, go to your insurance and claim you came out to the car being hit in a parking lot, and have no idea who did it, your deductable is most likely a lot cheaper then an OEM bumper cover, and the paint work needed.
The dealer will sell you the cover but its pricey, theres also the chance of getting a wrecked GT500 with rear end damage and salvaging it, or going with an aftermarket piece, but the easiest solution is saying you were hit in a parking lot.
2003 Redfire V6,
Show: Smoked everything, cobra front bumper, gt rear bumper, rear decklid and lower valence blackout with black mustang letters, 5% rear front 15%, black 98 Cobra rims front, 95 Cobra R rear black with chrome lip, black scoops and spoiler and exhaust tips
Go: CAI, True Duals with flowmaster super 44's, Bama Tune, full suspension (lowered, 8.8, 4.10s, UCA, LCA, springs, CC plates)