Hello Mirco, good luck visiting us in brisbane.
You may have some difficulty in renting a good road bike here.
there are a few places in brisbane that hire out mountain bikes and cruisers, a google search will locate these places.
but good road bikes - i think you are going to have to send a few emails
here are some suggestions, some of these bike shops have been known to hire out good bikes in the past but you will have to email them to see if they still provide this service.
http://99bikes.com.au/stores/fortitude-valley-bike-shop http://epiccycles.com.au/?page_id=29 http://lifecycle.net.au/ also there is a shop that recycles second-hand bikes.
they often have quite good road bikes available for sale and sometimes hire
http://www.bicyclerevolution.org.au/ Hope that helps, we can go for a ride when you get here.
Regards, Steve