If I was you I would go ahead and buy some aftermarket rotors. The thing to be sure about though is to get stock Isuzu pads. I have R1Concepts rotors and stock pads and all is good. However, I originally put the R1Concepts rotors on with R1Concepts pads and my brake performance was TERRIBLE (scary in fact).
I think as long as you stick with stock pads and decent quality aftermarket rotors will be fine.
Bart