These days color by number books can be found in various forms. You could choose among different fairy tales characters and/or animals, autos and so on and so forth. If your child is in love with Winnie-the-Pooh, then you may find a lot of colour by number games with the heroes of this toon.
Internet is a hub of free coloring printouts for kids. Parents or pre-school teachers can easily access a variety of such coloring pages. They can select the best ones for their kid after considering certain factors. Then they can take out prints using good quality printer. All you need is just a computer at your home.
It's hard nowadays to find ways to get your kids, especially boys to sit down and work on something. Harder still to find something you can do with them and really take part in and contribute to. This is a fantastic thing you can do today to bond with your son and I really recommend it. Oh and it doesn't hurt that its really cheap to do!