I'm going to say that the question as asked isn't possible in any conventional sense. Not only is the number of personnel larger than the active duty US Armed Forces, but it is a large percentage of the population of the nations in the region. That many people taken out of the productive economy would be immediately noticeable, even if they were somehow invisible to surveillance.
As well, the industrial infrastructure needed to build the weapons and equipment and the logistical backbone to support such a force would also be staggering, and quite noticeable (for example, Australia would be mining and exporting a lot of coal and iron ore in order to make the steel for the ships, tanks, trucks and so on, material which would have to be accounted for since it can be tabulated as it comes out of the mines and outputs calculated. Millions of tons of steel don't just "vanish". Add all the other materials, fuel, electrical power and so on and you have an insoluble problem.
However, the real answer is they are already there, in plain sight. A population can be aroused to fight an invader, and much useful equipment can be purchased "off the shelf". People can move around via cars, trucks, public transit, on foot, on bicycles etc. They can deploy to any point on earth by going to their computer and logging into the Quantas page (or any other appropriate airline), and can carry knowledge of how to purchase or build useful devices with them (no need to carry a rifle or rocket on the plane).
This form of warfare is evolved from insurgency warfare, and even in earlier iterations can be surprisingly effective. The Provisional Irish Republican Army (PIRA) may have had a few as 500 "shooters" at any given time, but hidden in the local population they tied up tens of thousands of British Army soldiers and massive police resources, while maintaining the ability to strike in Ireland, England and even conduct recruiting, fundraising, training and sometimes attacks in other parts of the world from the 1969 until they laid down arms in 2005. More modern groups like the LTTE, Al-Qaeda or ISIS have amplified this greatly and have taken entire armies and coalitions to defeat.
The name for this style of warfare is "Fourth Generation Warfare" (4GW) and its basic tenants can be summarized thus:
Fourth-generation warfare (4GW) uses all available networks -- political, economic, social, and military -- to convince the enemy’s political decision makers that their strategic goals are either unachievable or too costly for the perceived benefit. It is an evolved form of insurgency. Still rooted in the fundamental precept that superior political will, when properly employed, can defeat greater economic and military power, 4GW makes use of society’s networks to carry on its fight. Unlike previous generations of warfare, it does not attempt to win by defeating the enemy’s military forces. Instead, via the networks, it directly attacks the minds of enemy decision makers to destroy the enemy’s political will. Fourth-generation wars are lengthy -- measured in decades rather than months or years.
Col. Thomas Xavier Hammes-The Sling and the Stone: On War in the 21st Century
Provide basic knowledge, such as the handbooks being distributed in the Baltic States in order to counter Russian aggression, and a Casus belli, and there will be all kinds of people engaged in the struggle, from using cellphone cameras for surveillance, to providing space in their garden shed to store items to "chemists" cooking explosives for IED's and the small core of shooters taking the fight to the enemy.
They are already there, and you are looking right at them.
