There's some very useful info on this page
http://www.porsche968uk.co.uk/technical ... brakes.htmOr you could get some 2 piece disks made up. I spoke to these guys at the Autosport show last year and they said they could make some alloy bells up to any dimensions I wanted or I could send them a disk and they would copy it in a larger diameter.
http://www.compbrake.co.uk/brakes/rotor ... at_17.htmlNot a bad price for discs up to 335mm diameter but they start to get expensive bigger than that.
Let us know what you decide to do.