Most places should know Zimmerman.
Mine either came from GSF, EuroCan'tParts or Vee W Services (who'd be cheaper and betterer than ECP or GSF).
The big difference to other rotors I've seen is that they have vent holes around the bell, allowing for better disc cooling. By the sounds of it the Halfrauds pads are the issue here though.
How much 'extra weight' did you have in the car at the time? Weight has a big impact on brakes.