Today I got a reply from Hasbro, and it was only delayed because the person had been away for the last couple weeks.

The reason for the limited amount of restocking we've been seeing in recent months is apparently due to Hasbro moving their warehouse, which is said to have disrupted their supply chain... and it may not be back on track until towards the end of the year (which relates to what the original email referred to - a worst case scenario could see the last three waves not hit stores until next year, BUT, if sales are good, we could see them before the end of the year).

What I can quote from them, to help calm down the masses a little, is...

In summary, we will be getting all the later waves of Combiner Wars.
Now it's just anyone's guess as to when the remaining Combiner toys will show up in Australia.