JimD,
I am only going off what I have read on the internet. One forum contained blogs which linked Sano to both amp & accordion production. The same forum contained references to Zon-Rio, and some of the amps apparently bore that logo.
I can find no mention of Zon-Rio on a comprehensive list of Italian manufacturers, though I do not deny the possibility. In fact, the only references I have found for Zon-Rio are all on American websites.
Wobble,
I'm sure that JimD will get to the bottom of this conundrum for you. I have tried to help by providing the information I have found, but must bow to Jim's superior knowledge. Still, all that said, you may wish to follow your own lines of enquiry.
It does seem, however, that I am not a million miles from the truth, as Jim did say that Sano imported and marketed Italian accordions.
Kind Regards,
Stephen.