Oh, I didn't know the name for those: "possum scraper". I'll see if I can scare one up that fits, thanks!
A salvage yard or eBay will likely be your friend. Since few people like their looks, take them off and toss them in a junk closet, my guess is that the price of a "scraper" should be pretty reasonable. The tough part might be finding one that isn't too wide, as most of the larger bikes that use them have very wide tires, much wider than the rear tire of a Zero. (On a Zero, a wide one would likely act like a space shuttle drag-parachute and not do a thing for its battery pack range.) I would try to find one that came off of a dual-sport bike, something like an older BMW F650GS. I think my 1997 BMW Funduro had one on its rear wheel.
I just looked at a 2013 BMW full-line motorcycle brochure and noticed that not one of the bikes shown in the brochure had a "scraper" on the rear wheel. Since I am pretty sure that a couple of their bikes come with that rear fender, it would appear that even BMW doesn't like their looks and takes them off when they photograph the bikes for their U.S. brochure.