If you ring around the local paint factors you should find one with a spectra-analyser or a "brick" which they use to measure the pigment strength and content in the paint and then checks the results against a data base to get a match.
I had my HA van "read" and got a 99.7% to a Merc commercial colour So close that you can paint edge to edge.
Its best to cut the paint first with a good compound polish to get a true reading.
HTH Mark
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