If you are referring to the ones with a chromed lens, I don't know where to get these. I would think that someone has taken the standard plexiglass and applied the silver window tint film available to give that chromed look. Don't know if it's legal or not, but my experience is that Z cars are attention grabbers anyhow. The traffic police tend to "expect" us to break the law, as a result, they impose more stringent guidelines on us than on other vehicles. Couldn't tell you that it would be a sure fire ticket getter, but I take the attitude of being well within the law, so that they don't have a reason to stop me, let alone ticket me.
On the other hand, if you are referring to the Chrome Bezel Headlight Covers, these are either clear or smoked and have a Chrome Bezel much like the Jaguar XKE series. These are spendy and I've seen them available from Courtesy Nissan and another guy up in Canada.
If you get Sport Z magazine, there was a write up in the Winter 2000 edition on page 21, there is a yellow 280Z with the Chrome Bezel headlight covers. They really look sharp! In letters to the editor, Charlie Osborne from Kingston, Ontario with Zedd Findings. Ph: 613-389-1397 wrote in and identified himself as the source of these. I called him and they are about $128.00 each, so they are spendy, but the chrome and lens are first class quality. I also checked with Courtesy, and their price was like 139 or so each.
Anyhow, hope it helped.