I came across the Turbine Brake Rotors at the PRI show.
(My 1994 STO Mustang runs the 14in rotors from a 2007-up GT500)
http://www.turbinebrakerotors.com/steel_rotors.php
The STO rules say a 'ferrous' rotor is required and 1 or 2-piece.
(The rep at the show says a magnet will stick to the friction surface)