I think I have seen them for sale overseas from places like Efstonscience, however a quick google doesn't find any Australian vendors, and Efstonscience has stopped carrying them apparently.
I did find these ones, I don't know if they are within your budget:
http://gammascout.com/order.html
or you could build one, if you can get your hands on a tube:
http://www.techlib.com/science/geiger.html
(see
http://lndinc.com/search/?stext= for parts)
If you were to import, you might want to check with customs first that they wouldn't have a problem with it.
Good luck!