If your are interested in farming edible fish, the following site might be useful to you as it goes over a few of the more common edible farmed fish.
Here is one fish farm that supplies stock fish.
Be sure and check your local regulations if stocking a freshwater pond. Hope this helps.
I did not see that you were in Australia.
The following site lists various fish farms in Australia. Since they are fish farms, they should offer stocking fish for sale. A tour of one of these facilities will also help you breed these fish as well.
Here are actual fisheries where you can purchase stock fish. At least one does online sales. The others might offer telephone sales or possibly allow sales via email once you contact them about your needs.
This site states to contact them with your trout needs and questions but that trout will not breed in your pond. They may be able to help you with breeding trout if that is your aim..
Please respond on this question list if you need further information.