BMU & THM
GAM operates as "Stewart Aviation", "Commander Air" and "Reefwatch". Normal entry method is by invitation, i.e. someone in already is prepared to recommend you (and accept the consequences if you turn out to be a dud). Chief Pilot is Charlie Mogg, YBBN, but Gary Trench, YMEN is the man usually to give the nod.
So find out who's flying for them already and say hello as suggested, or visit YMEN. The aircraft are probably amongst the best maintained GA types in OZ. At one stage they operated an active hold file with seniority for vacancies.
THM, I think GAM used to operate a flying school under some name at Avalon or Point Cook, maybe instructing could be a leg in.
As for Cairns, as I said earlier, you are, because of experience requirements, more likely to finish up in GA there than start there. There are a lot of pilots waiting in Cairns, not as many as Darwin.
If you are "Up North" around March/April, the big experience is Prawn Spotting in the Gulf, Karumba, then Boroloola. AeroTropics, (C310/BE58/AC50), GAM (AC50) and other operators from everywhere join in the fun, the season starts April 1, but some preliminary spotting happens before that to suss out where the prawns are so that after the Le Mans start for the trawlers, they have some idea where to start trawling.
This is good multi time building, expect 7 hours stick time per day with exemptions for duty and weekly totals,but personal discipline needed as many aircraft are in close proximity using 250' vert separation, bit like gliders thermalling.
If you do get to work in Cairns, it's the closest thing to paradise you will experience in GA.