Correct...
Tempe Tyres do parallel buying on certain brands (to stay ahead of the competition).
Those brands include, Kumho, Falken and Continental.
Taleb Tyres do parallel buying on Nitto.
On a GT-R, I wouldn't compromise on lower quality than that.
If the Fed Gov't introduces a tax on eBay and overseas purchases (like Tire Rack), the prices will go higher.
As a stop-gap, you might ask any friendly importer if they have leftover tyres from grey imports, being careful to stay away from snow tyres.
Tried Skylinespares.com.au ??