To add on to what Anthony said, I'm not sure about how easy it is/if you can get it in Australia, but Ritalin (Methylphenidate) is very comparable to Adderall. I take 10mg a day for a sleep disorder I have (CFS). That is a very low dose, but it does help me to focus and stay awake during the day. If you, uh,... sniff it, then the effects come on much faster and are more powerful but don't last as long as if taken orally. And Oxycodone does increase dopamine levels but I would just be weary as they are extremely addicting. I know from experience. But I won't get into my history with opiates right now.
And this is not really a suggestion, more than an anecdote and a question. I dip Grizzly Wintergreen and always use it when I'm studying. I find it does help me to focus more (Perhaps just a placebo) as tobacco is a weak stimulant. But I have heard that dip/chewing tobacco is illegal in Aus? Is this true? I find that funny because I love everything about Australia but if they don't sell tins then I'm not there. Haha.