I'm not aware of any marine grade paint that comes in anything less than quarts.  You may have some luck finding a touch-up pen in a close color at an auto parts store.

CLC sells Interlux Brightsides. You could try getting directly in touch with Interlux Support and see if they sell sample sizes. I purchased some System 3 2-part LPU in 4-oz sample sizes some years ago and used them for touch-up and making custom colors.

Good luck,

Laszlo

interlux sells in units as small as a half pint....but only in limited colors.  so if you happen to have that as your color you are in luck...a link for these is below (this is just indicative, most major suppliers will stock the half pints)

http://www.discountmarinesupplies.com/Interlux_Topside_Paints-Interlux_Brightside_Polyurethanes.html?gclid=EAIaIQobChMIwI6-qIa72QIVxEwNCh0Udw76EAQYAiABEgILHvD_BwE

but if you can't wait to hit the link...here are the four lucky colors!

h

  Thanks for all the great help fellow boat people. You all rock!