Are you sure there is only one kind of slate in Italy? or it's a specific kind of slate named like that? In every country there are lots of slates. Few of them will definitely be good.
I know that UK has many, and so does China and Germany. Here in Greece, we have more than 10 different kinds. Most are used for decorative purposes, and few of them are actual finishers.
Not sure, maybe in some place there is some kind of slate that could be suitable for razors but at today we haven't found.
I live near the place where is mined the slate used for pooltable or blackboard as in the old school time.