Go to
http://www.brakesinternational.co.ukwww.brakesinternational.co.uk and order online; the prices are very good and next day delivery is quite cheap too. The discs are imported from Germany, the make is "BREMTECH" and appear to be very good quality. On a 205 I used to warp big brakes every track day before I bought a pair from there and they havent warped even after about 7 track days.
If you are getting judder from pad deposits on the discs, and you know for definate that you avoid keeping the brakes on when you come off track, I would look at different pads. Mintex Pads are very good for not letting deposits on to the disc that causes juddering. Im not really keen on Ferodo pads but some peple find they are fine. Not a fan of Tarox at all though!
Avoid cross-drilled ones, as someone already said they will develop cracks, and for £150 they just dont make any sense at all, as they will DEFINATELY crack or at least craze. A lightly grooved disc can be useful though to help deglaze the pad, but a good quality plain disc can be just as good with good pads.