Hi Laura, actually I do live in Italy and I'm a bartender, and I think that
you should tell your friend that "cassis" is the french word for
"blackcurrant" which in italian is called "ribes nero", in other words is
exactly the same thing.
I remember that to drink beer and blackcurrant or Pernod and blackcurrant was
very popular in England few years ago, but to tell you the truth I've never
dared to try it !!! like they say in London "it's not my cup of tea", however
tell your friend he can find cassis or ribes syrups in liquor or wine stores
all over Florence, unfortunately this time of the year almost everyone is on
vacation, so I couldn't get any precise info from my source in Florence,but I
don't think your friend will have any problems if he'll ask for "cassis" or
"ribes nero". I hope my infos have been helpful
Ciao
Dom Costa