No, mangos aren't all year round in equatorial areas. They normally fruit late dry season (winter) and early wet season (spring). In colder climates they're summer fruiters. The country with the biggest mango production by far is India, which is around where mangos originally came from.

I think you can find some varieties that will fruit off season -
I've heard ChocAnon and maybe Nam Doc Mai....

Mdoggie

That will happen in colder (marginal) climates, flowering can be initiated by fluctuation in temperature. Quite often though the flowers/fruit will abort later.