Unfortunately there just isn't a big supply of headlights for these cars as the production numbers weren't as high as the G35's and G37's. So you're left with either buying new ones from the various Infiniti parts sites, or used ones on eBay. Every now and then you can spot new old stock on eBay if you're watchful, but it's kinda rare. I think many parts sellers realize the high value of headlight housings and hold out for top dollar. At least you have halogens that cost a lot less than the factory HID housings ($1,500+ each!!)
BTW - after polishing, you can try recoating them with clear coat so as to retain the clear lens for longer. There are lots of videos on YT on how to do it.