Hi Giga,
Thanks for posting your question here. I just reviewed a couple of the most recent listings you have created through your Auctiva account and I was able to see the "Good 'Til Canceled" option within the "Duration" menu in each one, so it appears that you may have already figured this out.
For the eBay Australia site, this option is generally available to eBay Store owners listing in the “Fixed Price” format, as described on the following page of the eBay AU Help index:
http://pages.ebay.com.au/help/sell/duration.htmlIn any event, if you are still having trouble selecting this duration for any of your items, please contact our Customer Support team directly from under the "Help" tab and we will be happy to continue working with you.
-Mike