I bought a 350Z Roadster used roughly a year or so ago. Soon it will need to go through inspection, but the passenger side low beam xenon headlight is now out. Replaced the bulb and it did not help, so the ballast is probably shot from moisture.

Yes, this is the root issue I need help with. I am missing 2 of the 3 parts that shield the area beneath the front bumper and above the front wheels from road moisture. As a result, my passenger side headlight got water in it. Where can I find aftermarket replacements for this? Before spending the money to repair what is damaged from moisture in terms of electronics, replacing the shielding so to speak seems like a good idea.

I'm not sure exactly which parts you need. With your light problem I guess you're missing the liners in the wheel wells. Here's a link to Courtesy Parts for those (click on the Front Fender & Fitting diagram).

If you need the front undertray replaced there are a couple of fabricators here on NICO that makes a nice aluminium version to replace the plastic OEM supplied one, 350Z & G35 Aluminium Undertray and 350Z Aluminium Splash Shield. GT Spec also makes one, but it's a little more pricey and harder to track down...it's not even listed on their website.

CongratZ on the purchase and welcome to NICO!

Great information. Too bad no one fabricates the shrouds that go in front of each front wheel. I'd love to have those as well in the right material!