Doug,

You're best bets for that in the downtown area are The Globe and The Wall Street Cantina - both owned by the same management. The Globe has nightly outdoor music from 5:30 'til? and the Cantina has occaisonal outdoor stuff. They also own and operate One Eyed Jacks which has a stage area for indoor performances. Don't know who handles the booking or how far out they are booked. Give them a try. I don't play that kind of gig so I haven't dealt with them, but it seems like a decent set up. You'll need your own sound - they don't provide it.