cowboy mac posted links to australian psilocybin mushroom texts in this forum not too long ago... the psilocybin mushroom guide to australia and new zealand is not really very good to use for hunting however...
basically you've got to get out and about and find your own patches, but it helps to do some research on the mushrooms you might find - so you can look in the right habitat!
basically - nsw, melbourne (and SA?) during winter after rain, you'll find p. subaeruginosa and it's variants (p. australiana and p. eucalypta). these are woodloving and in the places i described above.
in the warmer months, in nsw and queensland you can look for p. cubensis and copelandia cyanescens. these grow in cow dung, and fruit during high humidity after rain. so basically you'll find them on cow pastures
i'm not sure how prolific these are down south... i found some on a trip to byron... but if you live in victoria, i've heard of people finding them but you might have some trouble (all the more reason to stock up on subaeruginosa in the winter!).
as far as potency goes, subaeruginosa are reportedly VERY potent, likely to be twice as potent as your cubensis, so be careful
finally, make sure you're 100% CERTAIN of an ID before eating your mushrooms! eating mushrooms can be dangerous, theres plenty of poisonous ones out there. if you're not sure, get a digicam or write a detailed proper description on the shroomery (not sure if im allowed to post links here, so just do a google search) in the hunting forum and you'll get lots of help there
cheers,
jimbu