I have ipad mini 2 or ipad mini retina but there is no FACE TIME where i can download face time application?

Where did you buy the iPad ? Some countries don't allow FaceTime, if it was bought from one of those countries then you won't be able to get the app (it can't be downloaded), including via iOS updates or if you move to another country.

Where was the iPad purchased?

If in a region where FaceTime is banned (Saudi Arabia, UAE), it can never have FaceTime.

The other iPads may have been grey market.

Facetime is built into iOS. It is not an app that you can download later on.