Welcome to the forum Netta, and in the context of where there's a will, a way can be found and we could say nothing is impossible, and a few points:
1. Main region for white water rafting is Cairns/Tully in north Queensland and it is a seasonal activity to some extent, relying on good wet season (December to March/April) rains to have suitable river flows - I'm not too sure how much they do in the wet season itself, and as you would be aware, too much rain and too high river levels can be dangerous, and business would certainly be less as not as many visitors venture to the north in the wet season.
2. I have seen reference to guide courses being offered for the intent of work to be had, but it could also just be another income for businesses.
3. Most work in the tourism industry usually comes from people being somewhere at the right time or before and willing, so if you come, head to the region and are willing - that's a start at least.
On accomodation, there's ample holiday type units up around Cairns, caravan parks with cabins etc. and being the start of wet season from when you arrive in Australia, quite possibly a good range of accomodation available, there also being many backpacker hostels in Cairns area -
BUG - the Backpackers' Ultimate guide to budget travel in Australia being a good guide.
There's
http://www.australiaforum.com/jobs-w...thunder.com.au where you can chat with a local Cairns tourism company operator and they may be able to give you some ideas from closer to the action.
There is also limited activity in rafting in other areas that may be more active than during the northern wet season as southern areas tend to get rain more in spring and thus with that and snow thaw (good snow season this year), there should be good river flows, thus: northen NSW coast (Coffs Harbour - northern rivers), eastern Victorian rivers (trips more than likely organised from Melbourne), north eastern Victoria, Mitta Mitta river and Tasmania could all be worth googling up to see if you can find companies looking for guides.