If there is a factory service manual for the Zero, I have never heard about it. I'd like to have one too, but usually motorcycle manufactures keep those things locked up for the layperson and only provide them to their authorized shops and factory-trained technicians.
A couple of years ago I bought an official BMW factory service manual, on a DVD, for my F650GS. It cost me $115. A year later, possibly after complaints from shop service departments, BMW stopped offering the DVD in North America. When I found that out, I asked my friendly parts guy if he could get me a shop DVD for my R1200R. He said wait here a few minutes. He went back into the shop, grabbed their DVD and copied it for me on his computer. I got that one for free - although it doesn't have the latest updates, which is one of the other things that BMW says they are concerned about when their wrench-spinning customers obtain one of their service manuals.