There have only been two main Zone of the Enders games thus far. However, Hideo Kojima did state a few months back that a new entry had entered the prototyping phase.
Could the project be called Zone of the Enders 3? That’d obviously make a huge amount of sense, but Amazon Italy seems to believe that this will indeed be its final name.
I personally never put much stock into retailer listings since they tend to be completely random and usually aren’t a sign of what’s on the way. But with a new Zone of the Enders game in the works… well, you never know.