Melv may be saying this in jest, but seriously.. have you looked to the pads to be the problem.. Discs rarely "warp" , the problem is usually down to pad material getting deposited onto the disc surface causing them to wear unevenly, or build up raised 'lumps'. The juddering is then due to the varying disc thickness as it rotates against the pads.
If it is this it will be due to the pads being too "soft" for the application and/or overheating.
What pads are they in there?

If you have access to the kit, take some measurements -
Measure disc thickness with a micrometer at various positions on an imaginary circle round the disc (ie at the same distance from the centre each time).
Then measure the disc runout near the outer edge of each face. Fit wheel nuts to make sure the disc is clamped tight and flat on the hub to do this. If the discs are really warped you should see the runout showing up at the same position on both sides. Be careful, because obviously variation in disc thickness can "look" like runout