Vincent Aviation in Darwin operate the 1900 along with Ad Astral in Perth. Apart from that they are not a very popular aircraft for the operators in Australia with the operating expense and increased cost of operating over something like a Metro.
There are a few Vans around, In Sydney they operate night freight with Jetcraft, Chartair in Darwin have them, Slingair in Kununurra, Polar in Port Hedland, Broome Aviation in Broome, Avwest in Perth. Not to sure about the majority over east but there is more than likely a few. Check the operators at every port from Cairns down.
Cobham are advertising for Dash 8 FO's right now, most aviation jobs are advertised on the Australian Federation of Airline pilots website.
With the recent collapse of Macair with Saab 340/Metro 23 pilots , the redundancy of 20 metro pilots from Pelair, Network laying of 8 Braz drivers, Ozjet ceasing operations with 737 drivers on the market and Skyairworld going belly up with E170/190 drivers floating around I think you'll be in for a tough time.
I hope the girl is worth it (or boy whichever the case may be)
Good Luck