ducatipaso.org

i've got a couple of front discs, they are about 4.9 mm thick and i dont use them anymore.

try VeeTwo (http://www.veetwo.net/store_bike.asp) and Gowanlochs (http://www.ducati-gowanloch.com/brembo.htm) in Australia. At least one of them used to have cast iron replacements and also a floating version of the 280mm disc. Can't quickly see them on their webs sites but worth a try.