I've been down this rabbithole recently.
First port of call is to contact the manufacturers to see if they can provide a paint code for the colour in question (standardised such as RAL or Pantone). If so you can usually get this mixed locally by an automotive paint supplier; although some codes seem off the menu - such as that for my Genesis (which is a RAL 7xxx code; while people only seem to do 6xxx)
Next option is to get some paint mixed to match the existing finish. Automotive places will have a colour sampler, which basically analysises the colour under known, calibrated lighting to obtain a match. Unfortunately for us this only works on largish, flat panels so our skinny tubes are off the menu. Again,
My local place took the last option of manually comparing the existing finish to sample swatches to find the closest match. This wasn't ideal, however was as good as it was going to get and unless you're really skilled with mixing paints I suspect far better than a mere layman could achive.. while they have literally hundreds of variations of one colour across a range of suppliers; rather than the handful you'll get it seeking a solution from something like model paint.
I paid less than a tenner for a sizeable pot of touch-up paint for my Fuji; which I thought was very reasonable. Now all I need to do is apply it to the frame without accidentally ending up with multiple green cartoon penisis smeared all over my face 🤞