The aussie ones are usually Tandanus Catfish, I think thees a few different species. I see them in the shops here but not too many people seem to keep them. Lots of people love fishing for them though, theres a place called horsham in the northwest of the state, the wimmera river runs through it and they say they catch them up to 50cm long. If I had a big pond id try to catch a few myself to throw in it.
If you want them for your tank they are cheap here, probably around $10.00AUD each for a 5cm one, I doubt too many people know how big they can get.