You can probably find a car paint factor in your area on the internet who will advertise they have a specrometer. This scans the actual colour of the car (or hubcap) rather than needing a colour code. Its particularly useful for matching paint that has faded over the years. . And many will mix up aerosol 'rattle cans'.
They are typically in small units on industrial estates rather than obvious retail shops. Take the car along and they will probably scan the hub cap still on the car and mix up the paint while you wait.
If you dont want to do this you could take a hubcap into Halfords (etc) to find the closest match you can from ready mixed colours,or by prior agreement they might let you take a few cans outside to compare. But it might not be much cheaper than having spectometer and custom mix can made up.
If you find the match is good but not 100% perfect you could spray both hub caps on that side of the car (or all 4 if you intend extensive wheel rotations.)
