"VMC Limited was founded in 1951 and was one of the first companies to Vacuum Metallise in the UK. With well over 50 years experience, we pride ourselves on the quality of work that we produce and on the relationship we have with our loyal customers. Based in Chertsey in Surrey, we are conveniently located less than a mile from junction 11 of the M25."
https://www.vmclimited.co.uk/
As fitted up until about 1973 part number 37H7034
The July 2020 Mini Cooper Register magazine 'CooperWorld' has a feature with photos on restoring the now rare early 1275GT Chrome eyeball air vents. After a careful dismantling process the bright finish was restored by VMC a company in Chertsey, Surrey using a process called Vacuum Metalising or PVD (Physical Vapour Deposition), the parts were returned in a week and cost was £100 for the pair. I guess this process could also be used on the standard black eyeball vents.