You can buy them from scarebird pre-drilled, or save a bundle and buy them locally. You get a paper template and they are not as hard to drill as you might think.
So the paper template is a joke its pain to get it to be lined up and centered. I used the old drums as my templet. I put the face of the old drum on the face of the rotor hat and used a center punch to give my drill bit a place to start.