I have searched the web from time to time for many years but never found anyone who offers a soft top for the Ritmo.
I have met one owner in Sweden who got a hood maker make a new soft top for his Cabrio. Great result.
I drove down to Italy in 1999 during Fiat's 100 year aniversary. I visited a Fiat part store there but they did not have souch parts for the Cabrio any more.
So as you say getting parts from Fiat today may be impossible.
There must be many(?) Cabrio owners around in Europe that's struggling with their old soft top.
What have they done? Is a custom hood maker the only solution?