I have an HR-4, and just bought another one. Great unit. However they are pretty rare, you don't even see Oz stuff on eBay very often. People who have them don't tend to give 'em up.
Do a search on Froogle, there are three or four online vendors of Oz stuff in the US.
6 channel hp amp, and i love it,
the connections are super, it looks great, goes loud as fk,
i do have a bit of basic humm and hiss but it definately is OK !
i'm not selling it, it rocks,
if u see one for second hand, go get it !