Hey Chris,
I am not really sure about close to north side of brissie. I have always had to do a bit of a drive to get them and it can be a mission to get to them. I usually drive my 4wd up the beach to find them. I find that you have to get away from heavily populated areas to locate good sized ones. You could try Bribie, I have never tried there before but they might be there. I would think a ferry ride over to the surf side of straddie might also be worthwhile but once again I have not tried over there either. Some one else here might know. Sorry I can't be much more help there.
When you do find them just remember that it requires alot of persistence and patience to get the technique right and it can be quite frustrating. They are quicker and stronger than you might think........you will see what I mean when you find them. Just remember to grab and lift in one smooth motion and wait till they are latched on to your bait and arching their back, they seem to release their grip on the hole when they do that arching motion.
If I get out for a day trip to chase them I will let you know but pretty busy now till after Chrissy.
Cheers,
Bill