I think with our proximity to Japan Australia has been blessed with having many Shihan visit or even stay and establish organisations. Old organisations tend to have a hierarchy and membership base to protect and need to have more 'boundary control' than younger organisations that open their doors to all. Of course young organisations get old eventually and might succumb to the former strategy.
With a little care its possible to practice with the greater majority of dojo and there are some fabulous teachers and seminars out there
There was a somewhat emotive discussion on the Aikido Australia email list last december (http://sports.groups.yahoo.com/group/Aikido_Australia/
) whilst maybe not so helpful at least you know you are not in the trenches alone. Here is a list of the major organisations in Australia. http://www.aikidorepublic.com/aikido-australia
PS where you off to Ronin?