i used some of that DupliColor Metal Specks on a computer tower about ten years ago (same color, too!) came out really well and looked similar to the Crook headstock (although still not as "sparkly".) it's just not possible to do flakes much bigger than "dust"-size with spraypaint cans, because they'd clog up the nozzle. i'd guess that even that Crook was probably done with a professional spray gun.
finishes are not something i'm particularly knowledgable about, especially anything other than the standard stuff. but as far as i'm aware, i believe there are two main ways metal flake is applied: the first way would be to mix the metal flake in with the color coat. the second way is to mix the flake with a clear and spray over (or under) the main color coat. sometimes translucent colors are used (candy apple red is a good example, as is Colt's blue Tele body above, of using translucent colors), and that gives the metal flake more "depth".
unlike shooting regular old solid colors (which is pretty straightforward), there seems to be about a dozen different ways to work with metal flake. it just depends on the type of metal flake you're using, and the effect you're after.