FYI, TireRack.com apparently has SC rear rotors (example 1990) from Brembo, Manufacturer Part #: 27100, on closeout for USD$20.00 each. Usual price: $35.00.
Select vehicle: ford/1990/thunderbird sc...then click on 'brakes' - look 1/2 way down on that page. (<--not confident this link is maintained across systems, etc., so YMMV)