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).
One great idea is the activity sheets based on the Disney characters and story behind Disney_Pixar's full length animated film Cars. Easily downloadable from the web, these sheets can be printed in as many copies to be repeatedly enjoyed by any school_aged Lightning McQueen fanatic.