How to get a smooth and glossy professional finish on plastic?
That may be the plastic itself rather than paint. Molding the parts using colored plastic and a mold with a mirror finish produces a surface like that.
Getting that kind of finish with paint basically requires &quot;polishing&quot; the paint.  It is sanded with extremely fine sandpaper (grit in the thousands), then polishing compound, and buffed. It's essentially the same process as painting a car.
If you need to do that with small parts, do the painting process as you've described. If there's a lot of surface detail, skip the sandpaper. You can use toothpaste as polishing compound. When you buff it, don't let the surface heat up, as that will melt the paint and make the surface a mess. Car bodies have a lot of metal to suck away heat, but plastic is an insulator and heat will build quickly.