Amazon is just a different version of eBay really.
You can use Amazon Australia but there is no benefit because of purchase cost. Items bought from Amazon Au come from Australia. Items from Amazon US, come from the US. Amazon US decided to block us aussies at the same time our grubbernment decided to make any seller outside AU pay 10%GST on any item they sell to Australia. It only ever used to be anything over $1000 as you would know.
Apparently, Amazon said this is why we cant use their US site. But it quite obvious that their AU site is a flop so they are forcing Aussie Amazon shoppers to use the AU site. All its going to do it make them switch to other sites to buy overseas. Like eBay...
So if you want to buy some chev parts. You would have to contact a seller directly I reckon and convince them to sell and ship it to you. It shouldn't be an issue for most sellers though.