Interesting discussion; here in the UK Anacondas are quite readily available, although mostly wild caught imports. They are nowhere near as popular as the large pythons because anyone wanting a large boid would have to wait 10 years with a neonate Anaconda, compared to maybe 2 to 4 years with the giant pythons. Plus there's a few misconceptions with their husbandry which leaves many trying to emulate their natural habitat in captivity which often results in poor levels of hygiene and dead snakes.
It is true they are docile (yellow anacondas are usually much more snappy and less docile in general) and have simple husbandry requirements - except (especially for females): living space. A 6x3x3 is NOT going to be adequate for a good sized adult female Green. They have massive sexual dimorphism a 6x3x3 is more than adequate for all except the largest male Greens, but a female Green, normally substantially longer and much bulkier would be very cramped...
In my opinion I would agree it would be naive to believe Anacondas aren't being privately kept in Australia. That said, there is probably only a slither of habitat in Australia that could support their living requirements.
