Published UK author Brian John has announced a competition in his search for an illustrator. Most of us won't be able to enter since he's looking for West Wales talent, but I do find his approach intriguing. He has published about 30 books under the Greencroft Books label (his own publishing house).
As more authors start considering self-publishing (because of e-publishing possibilities, print-on-demand options, etc.), this may be one way for them to find illustrators. Because an illustrator would need to be willing to do work on spec upfront, however, they may only attract less experienced illustrators.