Can I get an ebike with a 500 watt motor in Australia? I'm a bit on the heavy side, so I'd like to purchase an ebike with something a little gutsier than the usual 250 watt motor so that I can go up hills. Can these be purchased in Australia at all?
A 500W motor is not currently legal for use in Australia.

"In Australia the e-bike is defined by the Australian Vehicle Standards as a bicycle that has an auxiliary motor with a maximum power output not exceeding 200 W without consideration for speed limits or pedal sensors.[1] Each state is responsible for deciding how to treat such a vehicle and currently all states agree that such a vehicle does not require licensing or registration. Various groups are lobbying for an increase in this low limit to encourage more widespread use of e-bikes to assist in mobility, health benefits and to reduce congestion, pollution and road danger. Some states have their own rules such as no riding under electric power on bike paths and through built up areas so riders should view the state laws regarding their use. There is no licence and no registration required for e-bike usage.

Since 30 May 2012, Australia has an additional new e-bike category using the European Union model of a pedelec as per the CE EN15194 standard. This means the e-bike can have a motor of 250W of continuous rated power which can only be activated by pedalling (if above 6 km/h) and must cut out over 25 km/h – if so it is classed as a normal bicycle. The state of Victoria is the first to amend their local road rules, see below."

Quoted text from https://en.wikipedia.org/wiki/Electric_bicycle_laws#Australia