Hi Spirit, the discs are custom items made by CAT Engineering in the UK. I sent in two standard CB750 discs and they machine off the rotors and then cut 4mm cast iron discs and graft them on. The disc rotors are cut off a 295mm diameter cast iron "bar" that weighs over 50 tonnes when new! They aren't cheap but I have to say I run one of these discs on my black bomber racer and it gives awesome stopping power.
Source for tanks and oil tanks - you can get them from MeadSpeed online but they re-sell Bartell tanks with a mark-up. If you google Bartel engineering, Donaghadee in northern ireland you can get a phone/fax and deal direct for less cost. The proprietor, Asa Moyce is an ex-Honda racer and is superbly knowledgeable if you have any questions...