Try Kehi Lagoon, or La Marinana (right next door to Kehi). These are usually your bet bets unless you are a DoD ID card holder and can get into Pearl Harbor. There are also a number of balls to moor up to around Kehi. Ala Wai is not going to work out for you, and you'd be lucky to get a transient slip there, though it couldn't hurt to ask. Ko Olina is nice, but get ready to pay. If the boat is small enough, you may consider Waianai Small Boat harbor. 10 year waiting list for Haleiwa on the North Shore so I would bother with them. Finding a slip or mooring is possible, just takes a little looking into.
Lack of moorage is the biggest hurdle for potential boat buyers in Hawaii. The state is HORRIBLE at allocating their funds so they let their marina fall to pieces. Waste of a natural resource for the state, but you'll soon see why things are so mis-managed after talking to a couple DLNR folks there. Best of luck!