First of all, I'm not available to co-author a story with you.
As an attempt to help out in some other small way; what specifically do you need in a co-author? Are you supplying the ideas and the other does the legwork of writing them down for you, much like a ghost writer? Are you looking for someone to brainstorm with you, to help fill in the gaps of you story idea? Is the idea you stated above pretty much all you have at this time?
Answers to these questions might help someone who is considering your request.