I know what you mean aus tandem. Finding a tandem on sale here is difficult; finding a good tandem is even harder. Having had our Apollo for 5 years now and with a second child on the way, we will have to consider what to do later.
I would have thought there would be Trek or Cannondale dealers relatively nearby - Sydney at least. However, Zonatandems idea on a framebuilder may be better (Hillbrick is the only one that springs to mind in NSW). There's one framebuilder in NZ (the only one that I can find) and I think that's what I would consider when we buy another tandem.
Good luck with the search.