From time to time I get asked where I found the drilled rotors for my bikes.
Here is the answer ; take your time and layout a nice even hole pattern. Make sure your holes intersect slightly so you don't get much striping. Use a drill press and take your time.
I get asked if I can or do drill these on the CNC and the answer is -No. It would take longer to set it up then it would to just do it and it is not near as difficult as it looks. If you want some layout tips , the best one is to find a rotor with the pattern and the size you want and just transfer punch it onto yours. With some layout dye, a steel rule and a set of dividers I can usually layout something in about a half hour. Don't be afraid to play around with it, as long as you are pretty balanced and don't remove more than 30 or 40% of your braking surface area you should be just fine.