Check art schools in your area. Art students are often willing to work for free or for very little in exchange for seeing their work published. It will strengthen their portfolio and make your self-published book come to life. Check school bulletin boards and websites for talent.
Search art websites that offer copyright-free or public-domain images, illustrations and photos that might suit your book. These include Art-3000.com, FoundMyself.com and DreamsTime.com.
Visit art fairs, galleries and shows in your community. You might meet an artist or get contact information for several. Artists are usually responsive to collaborations. If you're enthusiastic toward their work, they may want to contribute to your book or help you find a colleague who will.
Post messages on social-networking websites like Facebook, LinkedIn and Twitter, stating that you are looking for an illustrator for your book. Send a message to an artist you would like to work with who is already using one of these sites. If an artist turns you down, move on to the next one.
Visit local bookstores. You may find a notice board or fliers containing contact information for illustrators or other creative people who may help you find an artist.