Many professors have email boxes that fill up faster than they can clean them out. There is a lot of semi-academic spam, much of which seems to originate from developing countries... new "open access" journals, conferences, opportunities to join editorial boards, post-docs and students who spam half the continent with their CVs without any regard for what the professor actually does. I'm NOT suggesting that you're one of these, but it's quite possible that if you've only tried contacting a handful of professors directly, you're either getting screened as spam or just plain ignored as a result of association.
Most schools will have a point of contact for prospective graduate students - sometimes it's a graduate advisor or a department associate chair. The point is that there is a person who has at least some time specifically dedicated to interacting with prospective students. You may have more success getting a response from someone like this. They can also be in a position to arrange for you to speak with professors who work in the field you're interested in or give you insight into whether a particular professor is even taking any students in the coming year. Remember, they don't always have the capacity to take on a new student.
Getting into graduate school is a highly competitive process, even among applicants from within the school's country. So if you're not successful there could be many reasons for it that have nothing to do with where you were educated.