The online tool has been hopelessly buggy since the day it was rolled out. There's a whole sticky thread on this - xONEx online tool bugs thread - FlyerTalk Forums

As for availability to/from Oz, note that the Oneworld Explorer books into "L" class in economy and "D" class in business, and some airlines (cough, Qantas) can be very stingy in releasing L or D seats into inventory during peak periods, such as the holiday/southern summer season.

Your best bet is to ticket through one of the participating airlines, of which AA is the most experienced via their RTW "desk." If you're in the UK, I'm not sure if BA still has any bespoke staff for RTWs, but it's worth a phone call.

Oneworld itself has no customer-facing services.