IIRC when I was looking 18 months ago I couldn't find any readily available equivalent. 305mm dia. means they're not exactly common. Some folk use spacers to move the caliper out to suit 320mm discs and this was the route I was going, albeit using a single 320mm (as per the Hyper prototype) and new master cylinder, until I found that 'older' versions of 305mm Braking discs were available at a reasonable price on Italian EBay. Only a minor redesign of the carrier so I bit the bullet. I think Galfer also do a 305mm set but have seen one or two reports on Ducati.ms of people having warping issues with them.
eg
http://www.ebay.it/itm/COPPIA-DISCHI...em418d db4a33 About £230 inc post. Later design about £70 more...