You might try ebay first, I often see these listed. The 260z rpm gauge should be the same as the 280z (US version).
If you don't have any luck there, you could try some Zcar wreckers in Australia.
Try looking in these sections:
http://www.viczcar.com/forum/index.php/board,9.0.html
http://www.viczcar.com/forum/index.php/board,20.0.html