FaceTime is not available in all countries. It is blocked and you will not be able to get it via iOS updates. The best solution is to buy from a country where FaceTime is supported. However, there are some disadvantages of this option. Please read this Q & A to learn more.
Home / Q & A / Daily Q & A: I bought an iOS device [iPad, iPhone, iPod] in Dubai, and there is no FaceTime installed. How do I activate and install FaceTime?