Probably the easiest way to get a hold of pages for your kids to color is to print them out from websites online. There are plenty of sites that offer free downloadable coloring pages. Just search for "Christian coloring pages" or "Biblical coloring pages" in your favorite search engine, and you will find a bunch of results.
There are so many different pictures available that you may have better success using specific terms like "Jesus healing the blind man coloring page" or "Tower of Babel coloring page," as examples. This is a great idea if you are looking for a coloring page to compliment your evening devotions or a Sunday School lesson at church. In those situations, you can let your children color in a picture that represents the Bible story you are teaching them. After they are done coloring, they can tape their picture in their bedroom, which will help them remember that particular Bible story.