Stevia is an herb grown in South America. It has been used by native South Americans for hundreds of years to sweeten just about everything. Stevia is MUCH MUCH sweeter than cane sugar so you only need a tiny little bit to do the job.
AS FOR USING ONLY THE LIQUID FORM, that's not true. Dried or Powdered stevia is perfectly safe to use. The liquid form is a comparatively recent innovation, and indeed, there is some concern among knowledgable herbalists and researchers that the highly concentrated liquified herb preparation may present some health dangers not previously seen with the dried or powdered herb (the added ingredients to liquefy it may actually change the nature of the herb.)
There are two links from which you can order stevia in my blog article:
http://motherearthtreasurechest.blogspot.com/2008/08/fructos
I do not know about in Australia, but in the US many herb shops/health food stores sell stevia both in packaged form and in loose powder that can be bought in bulk. Stevia can also be found in grocery stores, but only if it is labelled as a dietary supplement rather than a sweetener.
Sincerely,
Tre