You are very limited in alternate options... basically you are either going to carry the fuel for the nearest major airport (IE Adelaide or Sydney for Melbourne, Melbourne, Brisbane or Canberra for Sydney etc.), carry fuel to one of the smaller "fair weather" alternates (if you can get permission) like Avalon, Pearce (mil), Williamtown (mil), or just arrive based on a "DPA" where you aren't going to have full alternate fuel.
Whatever complies with the airline/regulators fuel policy!