If you like your fish still swimming just before you buy them, I've tried the fishmongers in Chatswood (just outside New Yen Yen Supermarket in Help St), Willoughby Seafood (Penshurst St), Eastwood, Carlingford and of cuz Cabramatta. All good (taste, price, variety).

Thanks Jackie C, you've covered the north, north-west and south-west of Sydney, often overlooked as people flock to the SFM.