Hey mate,I wouldn't say there are any real 'secret' spots on where to find kingifsh, though some areas might prove to have kingfish frequent them more often. What would be a good idea is to understand why king fish would be in that area in the first place. More often then not they are out searching for a feed, so looking for areas that are likely to hold baitfish might be well worth a shot of trying for kingies. These areas, can include wharves, rockwalls, or even moorings. Baitfish congregate in the areas for protection and fish such as kingies are there for the hunt. Some people believe you need to fish deep water too, but I've seen kingies swim into the shallows at clifton gardens in no more than a meter of water chasing baitfish or hovring over shallow kelp beds in search for some squid.
Some guys have mentioned a few spots and I've seen kingies caught at pier 2, balmoral and clifton,. These areas do get very crowded, so might be worth a shot going for a drive one weekend and looking for areas that might hold baitfish and have access to deeper water.
Good luck
Joe