Trackers
As usual a large part of the solution is sitting on the doorstep, unseen by most. Wunwing is right .... convert the 11 idle sitting Trackers to Conair or Marsh Aviation Firecats (different engines & STC's) and you have a good base fleet of tankers that can deliver reasonable size loads with great agility and precision.
You would have all 11 Trackers modified for $50 million or so and the fleet would last for at least 20 years. Maybe a deal could then be made with CALFIRE to move some of their aircraft from California to Victoria in the southern summer and vice versa for the northern summer, so that effectively the tanker fleet of either state is greatly enhanced when it matters. Choosing the Marsh Aviation modification for the Trackers would ensure equipment compatibility.
It is nice and spectacular to see a widebody tanker, and certainly it will do some good, but to a certain extent it is only political grandstanding. Australia needs a fleet of dedicated tankers to fight fires from the air to begin with.