Robinson Racing and Precision Racing make good pinions among other companies. I'm pretty sure almost all will be aluminum though. This is a very advanced high end kit, so they probably assume you know some things already. If you haven't already, check out the first page of this thread because it has links to great videos to walk you through the build process and answer any questions you may have. While you are online or at the hobby shop grabbing a pinion gear invest in some new ball cups (jconcepts, RPM etc.) and a couple sets of front arms for while you are learning the car.