Actually cockatiels are classified as cockatoos, which is a very different branch of the parrot family. But bird food is generally classified by size not by family relationships. Mango can certainly eat cockatiel/small hookbill-sized food.

There are basically two different types of bird shows. There's the exhibition type, where people bring their birds to compete for prizes for who's got the best bird. They usually don't intend to sell their birds, although if they're breeding a show line they might sell or trade some of their 'extra' birds. Then there's the selling type of bird show, which is more often called a bird mart or bird fair. That's the one where you've got vendors selling birds and supplies to the general public.