"Need a small quantity of British racing green gel coat for a deck repair on my Pintail. Any ideas?"
Dave, if you don't want to buy gelcoat you can use epoxy thickened with colloidal silica then tinted with resin coloring agents.
As suggested by Gerry, just mix blue and yellow pigments until it matches your British racing green Pintail deck. I put wax paper on top of the thickened and tinted epoxy repair and if lucky very little, if any, sanding is required. Good luck on making your vintage Pintail look great again.
The Connyak BBS