Talking about spray paint, good old Montana Cans come to mind. They have the broadest range of colours, i believe. And primers for all sorts of stuff. They have various "effect" collections (stone, metal, etc.) and are not too expensive. Marabu is the cheapest and sometimes surprisingly best, but i don`t know if they sell those outside Europe.... But if you want a custom made colour than you`ll have to switch to acrylics.