Since I have publishing a book in mind too,I consider the following options
Either I �ll buy copyrighted material that will allow me to use the drawings for commercial use
Or I �ll find an illustrator as suggested by libertybelle
Or create my own drawings,the other day,while searching for a coloring page in vain,I made up my mind to draw it myself and you know,it was not bad,it was simple but cute,
In my case when I fail to find a material I �m searching for I start making and creating my own one:)
Good luck with your book,
And let us know as soon as it �s published