I recently visited both the La Sportiva NA and La Sportiva Italy websites and noticed that there's a much wider range of boots listed on the Italy site than in the US. E.g., the US site lists only the Nepal Evo, whereas the Italy site lists the Nepal Evo, Nepal Extreme, Nepal Top, and Nepal Trek. These aren't just different names for the same boot, they're different boots. Unfortunately I don't know how to buy boots other than the Evo here in North America, though you could certainly try ordering them from Euro retailers like Tiso (which I notice has Nepal Extremes on sale now), which may or may not be willing to ship them to North America. Or you could scoop up a pair on your next trip to the Alps.
I'm actually curious - who are all these different models targetted at? Are the Nepal Extreme or Top better suited for certain purposes than the Evo? Is the fit significantly different?