Hi,
These are a little hard to find, can get them on old HP equipment at times. Mouser still shows it in its catalog -
http://www.mouser.com/catalog/637/1093.pdf - it is known as a PH-163 connector and this cable I think is still made by Volex. No idea of pricing though, but this will give you more to search for.
-John
[Edit] I am not familiar with the Celestron C8 - if it will run from 240V 50Hz because the cable plug looks like it is for 110V 60Hz. If you bought this locally in Australia, then quite possibly it will work.