First, take your time

How about Putting an ad in the local paper.

Audition a few, and then when you've found someone appropriate and fresh and new, who doesn't try to bullshit you with jargon or "industry" speak, but has a bit of vision, arrange the terms of a collaboration, get it checked by a lawyer friend (or read about copyright etc) and then try to get it published.

Should be pretty simple, 50/50 I'd have thought for writer and illustrator.

If it doesn't work then you have your own unique copy for free ;-)