I use one of those minnow traps that I got over at Nakno's in Kaneohe. The kind with a funnel at each end. Best place I've found is the canal that runs out of the Kailua Swamp. Over by Pali Hwy in Kailua town. Cross the bridge at Windward Boats and turn right. I go by the Creek Side Tavern and Times Cafe.
Takes about 10 minutes to catch more than I need.
Another spot is that canal that runs right beside Ala Moana Blvd. in Ala Moana Brach Park. Loaded.
Mostly I "catch" my live bait at Moanalua Pets over by the Ice Palace near Aloha Stadium.