Can't help you out with GPS and probably not Jew but maybe barra and others. I can tell you that there's plenty of jewie hot spots in the harbour though! Best bet is to pop into a tackle store and ask them for some info. For barra, there's a spot called stokes hill wharf in darwin. If you troll hardbodies around this massive structure you should get Queenies, Trevally, Mackerel and the odd Barra. There are also a few nooks worth a cast for barra. The barra hold up here under the wharf. At night if you shine a torch underneath you can see them! Some 100+ in the mix too! Another spot i came across was the foreshore directly infront of the esplanade. Here the banks are very rugged made out of rock and mangrove. The dirty water here seems to fire them up too! Casting big lures and livebaits in is the go here. Some big fish are caught here at times so have the right tackle to stop them!
Other than that, i can't really help with any more spots. Let me tell you, there are no shortage though! For the barra things to look for are; Rockbars, Drains (Little streams of water flooding off sand flats into deeper/murky water, creek junctions and small creek mouths on the run out tide! I would certainly recommend catching some live mullet, garfish or herring for bait. It'll really boost your chances! Look out for crocs and BIG sharks! Plenty of them! Trolling lures around rockwalls and structure will always see if the GT's or queenies are around too!
Cheers, Tom