I buy seeds from both the British Iris Society and Species Iris Growers of North America (SIGNA), each year. The packets are always opened and approved by quarantine.
I have a friend who had a minor problem with one of her SIGNA orders one year - basically it was a packet containing 'mixed' Pacific Coast iris seeds. They ended up letting them in though.
You need to be importing in only small, non commercial quantities.
It needs to be from plants that are not on your states banned list, or a noxious weed.
The seed needs to be very clean - no husk, dirt or insects. Seed must be one species only, not mixed.
The individual seed packets need to be clearly labelled with the contents, by botanical name.
The outer envelope needs to state clearly the contents of the package, and that it is non commercial, or of minimal value.
If you bring seed in from companies or groups who are experienced in packaging and labelling seeds, then you shouldn't have any trouble. If you are looking at having individuals, say from the garden web forums, send you seed, then you may have trouble.

Cheers, Jan

you may want to try the following link, oh and be carefull to read the fine print as always. www.aqis.gov.au/icon32/asp/ex_alertscontent.asp