Sounds like you're talking about the backing plate or dust shield. I know Dorman sells them. But I'd Google "89 f150 4x4 front rotor dust shield" for new. As for used, most salvage yards would use a description instead of a part number. If I recall correctly, the original Ford base part number is 2K004 R/H and 2K005 L/H and probably fit various Ford truck sins.