The tooling you are asking for is not easily available. The Tools that are available Phil Wood Spoke Machine and the Morizumi Spoke Machine are both quite expensive and neither of them have the additional dyes for handling 10g spokes. You might have better luck contacting a supplier like Buchanan Spoke and Rim, Inc.
or The Wheel Master
to see if they could provide you with the proper length spokes.
One other thought about your project. The idea of using radially laced spokes on a rear wheel of a motorized bicycle in my opinion is a very marginal at best.