There is a farmer's market on Wednesday late afternoon at the Blaisdell Center lawn. It is still relatively new so, I'm not sure how large it has grown.
http://www.yelp.com/biz/honolulu-far...ket-honolulu-2
The farmer's market at Kapiolani Community College on Saturdays is a good one to go to if you have the time. It's just outside of Waikiki.