I'm not sure how many positive responses you'll get. From my experience, most iPhone devs either have their own ideas or have contacts with proven, professional design records.
I'd be genuinely interested to know if anyone takes you up on this offer. I think you're likely to have to give up a hefty percentage of the revenue stream to even get someone interested.
It's also a potential hassle to administer. Are you looking for someone to become a partner, or a one-off fee?
Your best bet is to make friends with someone who has coding ability, or to learn a bit of coding yourself and use something like Corona or Unity to code the thing up and outsource the art rather than the programming.
Good luck, anyhow.