From my limited knowledge and experience, these weren't sold in .au.
If they were, they were sold in tiny amounts, as TSHORBA says:
Intersound J1/J747 Super Jumbo
Conion/Technisonic TC-999
Panasonic RX-7000
Toshiba RT-S90
Sharp VZ-2500
Sharp GF-999
Crown SZ-5100
Realistic SCR-8
Toshiba RT-S93
Crown CSC-970
Sony CFS-99
RISING 20/20
Aiwa CS-880
Panasonic RX-7200
Toshiba BomBeat 40
Telefunken Studio 1M
Plus, as TSHORBA says, every Lasonic and the M90
Members have been known to pick up one of the above in their travels, but this doesn't necessarily mean they were sold here. I'm convinced the odd rare radio that turns up on ebay or a local find was brought over by someone who emigrated to Australia. None of the above models have ever been found locally by collectors in numbers greater than 2 or 3 in the last 5 or 6 years. For instance, AZA picked up an RT-S93 (the Toshiba with the remote) but thats been the only one ever found by any collector locally (that's been online anyway!). I think that pretty positive proof they never got sold over here.
With my own observations and talking to longer term collectors over the last five years, I'm certain that if these models indeed were sold over here there would be more than one or two reports of them through here and ebay over that period.
Of course this is just my opinion, but I'm convinced after what I've seen and heard over the years.
Another thing to look at when collecting, and this is just another of my theories, is geography. Much like the U.S where these radios turn up consistently is pretty well based on where they were solid originally. The big cities where boomboxes were populalr prove as rich hunting grounds, and other places that weren't so affected by street culture are more sparse, this is the same in Australia, but for different reasons.
I'm convinced the places where there was or still is heavy mining or work that required people to travel to for extended periods are the richest places for finding vintage boomboxes. Mining jobs are very well paid and workers would've bought good quality portable stereos to use while working away from home for months at a time. This explains, to me anyway, how so many boomboxes and grails turn up in the west where our mining communities have been established for a long time. For those unaware of mining in Australia one of the main locations is in and around where AZA and Shane live.
Lots of families would have emigrated to Australia from other countries for this type of work too, bringing with them the boombox that would eventually be sold off second hand, or at markets or such. The point is they'd HAVE to be in the area to begin with during the hey days of boombox production for them to be found there now. Of course boomboxes were sold every where during the late late 70s onwards but I think there had to be regions where they sold a lot more than others that would then explain why there plentiful in some places and scant in others. In my town, the second biggest city in my state, there have been very few big grails found, or sold through on ebay. I think back to the times in the early 80s and I for one never ever saw anyone carrying one around, and also Geelong never had any of the kinds of electrical retailers that sold these models. I remember seeing catalogues from more independant retailers in Melbourne and seeing lots of killer boomboxes that were never sold in my local stores, back then I used to think (and still do!) twin antennas were the hallmark of a true classic boombox, and I never saw one of these in person at any local electrical retailer. Not saying they weren't ever, but a lot of the great models I've seen sold in Melbourne hi fi stores (like TSHORBA posted a while back) were ones I've never ever seen sold on ebay, or at flea markets, or through tip/dump shops in my town. I think the models had to be sold in decent numbers in the region your looking for them originally for them to still be there now.
Based on this theory, I think areas like Broken Hill and Mt Isa and other established mining towns will be the real boombox paradises in Australia. Being inland and massively isolated I think they'd still be there as they would've been taken there en mass since the 70s.
Saying all this though, I'm still convinced a good 80% of all the boomboxes in Australia are sitting out in retired dude's sheds tuned in to some AM talkback stations after the kids were bought them new in the 80s, and then once the belts deteriorated in them was relegated to their dad's shed cause it 'still works and we paid too much for it to throw it out'.
These are just my ideas, I can't back any of this up with solid facts and numbers, but based on where the biggest collections are in .au and where we find or don't find boomboxes I think it's something to at least consider.
Rock On.