If they cater to the nitro-power RC buggy trade at all get a bottle of that stuff and doctor it up with enough castor to bring the oil content up past 22%. That fuel will tend to lots of nitro and not much oil, so after you finish putting in enough castor you'll definitely have more fuel than you started with. My understanding is that you really want "de-gummed" castor, but drug-store castor has worked for me.
The better quality of motorcycle racing shop will have castor oil, at lower prices than the drugstore. You can tell if a motorcycle racing shop is of the better sort by asking them if they have castor oil -- if they say yes...
In the US, Sig has castor for $23/gallon, and I don't believe that it gets charged a hazmat fee. But I have no idea what the situation is in Oz.