just looked on cabela's website and they have several models, including an 18". I think the top is smaller but may be able to get at least some hoops in there.PLUS, just ordered a Lyman 1200 Pro Tumbler, $66, and going to get some reptile bedding aka walnut shells. Researching the ammo reloading folks was helpful! I'm sure you could find these in Australia.
Don't forget to buy some polishing powder/rouge! That's the other part of the media formula/mix.
http://www.harborfreight.com/rock-polishing-abrasives-30956.html
John