I know, it's an old post but I finally found the original air vents and chromed air vents used by Lotus and Venom.
They are made by Alfa Romeo (!) and used on older Alfa 147, 156, 166, Spider and GTV. And now Alfa uses them again for the new Alfa 4C coupe and spider.
Alfa made two identical versions of it in the 90s, with and without a chrome ring. The rings are not sold separately.
You can still find new ones with chrome for only £9.99 each ! (New & Genuine Alfa GTV & Spider central air vent in black & chrome 113338560 | eBay
Lotus uses the one without chrome for Elise and Exige and with chrome on Europa and Evora. Same one is used with the Venom GT.
Old Alfa 166 and new Alfa 4C: