First off welcome to the forum, hope this helps.
You are not going to find the exact paint, in 77 depending on what color your truck was it might have used lead in the paint, which we all know is banned now. Now they use chrome-molly (or alloy I forget which one) to stabilize yellow paint now. (which yellow is in a lot of colors).
Acrylic enamel is the more traditional option that was used on older cars. Auto manufacturers and painters have switched over to urethane paint, as it provides numerous practical advantages over acrylic enamel for most auto body work.
" Although it is difficult to replicate authentic factory paint nowadays, and neither acrylic nor urethane paint offers that option, many car restorers argue that urethane provides a nicer-looking finish. Urethane paints are extremely durable, and resist chipping—when properly maintained, a coat of urethane paint will outlast most acrylic paints. "
To read the whole article see this:
http://www.thomasnet.com/articles/plastics-rubber/urethane-acrylic-automotive