I know the Acorn
Archimedes runs RiscOS, but what else? I'm not sure
that the Acorn was ever even sold in the US.
As far as I know it was not. My first exposure to the Acorn
machines were those brought over in '87 for Apple's first
attempt at a RISC Apple II (Moebius).
I never saw a RISCOS machine sold here.
I've found a few of them on eBay for CHM. Shipping from the
UK is painful. I've also had an unusually high percentage of
them never arrive.