For something as large as a seat, I would try find some space in a shipping container. It will take a while, but it is about the only way I know of that won't cost you a bomb.
I haven't gone via the container route yet but last time I almost did I contacted Ray Flaherty of Junkyard Classics (sorry but I cannot find his number) in Sydney (Smithfield if I recall). There are a number of other people who do this (I am sure the other members here will chime in with suggestions). Also, from what I recall one of the Chev clubs might have brought in containers periodically from what I recall being said by a visitor to one of our meetings a few months back. Can anyone remember any details?
I don't know how you would go with duty and GST if you go the container route but for something as large as seat I would expect customs to slug you. What you get charged depends on the item but from memory it was around 20%. Customs will tell you exactly what you would get charged for if you give them a call. In my experience customs doesn't care if you are a company or an individual trying to save a few bucks, as I have been told by a customs employee previously "If we think there is more than $50 duty to be made on an item we will process it".
Hope this helps.
