Your post did not list the locations near Brisbane and Cairns.
Both cities have light pollution Cairns is much smaller than Brisbane. Both have accessible locations where you can get dark skies.
I can give you two recommendations in the Cairns region.
During the 2012 solar eclipse I found a large area off the Mulligan Highway. It's a bit of a drive in but once there you can drive in off the highway. It is private property but treat it with respect, don't draw attention to yourself and you'll be fine.
It's located here :
.......o.....'......"
S.....16...14...30
E...144...43...33
Drive inland from Port Douglas to Mt Carbine. Zero the trip meter at the Mt Carbine Hotel. Drive 65.6km inland on the Mulligan Highway and you are there. It's a long way from any source of light pollution and up on the tableland away from sea mist.
You might also want to visit the lava tubes at the Volcanic national park at Undarra about 220km southwest of Cairns. The lava tubes are fantastic. You can stay in onsite accommodation (railway carriages converted to bunk rooms) or camp in the campground with your own camping gear.
Members around Brisbane can probably advise you better around Brisbane.
Most of Australia has easily accessible dark skies. Northern Australia has by far the statistically clearest in July.
http://www.bom.gov.au/jsp/ncc/climat...eriod=jul#maps
The area south of Darwin around Katherine & Kakadu has the clearest skies in Australia during July (≤90% clear).
Cairns ≤ 60% clear.
Brisbane ≤ 60% clear.
Southeast Australia ≤40% clear.
If you are thinking of visiting Kakadu, Katherine Gorge then this is going to be the clearest skies you can expect most nights to be clear. The coastal strip from Cairns to Port Douglas to Daintree is cloudy even in winter.
Joe