You can of course buy books preprinted with word search puzzles. While some of these books are very good, the disadvantage is of course you can't choose what words should appear in the puzzle. Another idea is to use your computer _ with word search maker software, you can easily create your own puzzles _ that way you can choose words appropriate for the age level of your children (perhaps even choose the words they need to learn for school spelling), and tailor the puzzles too (for example by avoiding difficult diagonal words if creating puzzles for younger kids).
Meanwhile to tickle the right side of the brain, there are numerous line drawings of each of the popular Cars characters that are available from various internet sites. A printer and scanner if available can translate these into hours and hours of creative silence. Copies can be duplicated in as many times as the child wishes to enjoy the pursuit, perhaps using and changing colors on the same picture as he pleases. These same pages can later on, with some help from mom or dad, be cut out and turned into an improvised jigsaw puzzle. And while on the subject, the same cut outs can be used as wall decors for the child's room, or as colorful covers for their notebooks and folders.