Why can’t I get the Happiny to evolve

The mega stone that evolves Charizard into its black Fire/Dragon type mega evolution can be found in Pokémon X.

It can, however, also be traded over to a copy of Pokémon Y and used there.

Source, more information

Its Lumiose City style, which is completely different than the style your clothing gives you. You have to max it to gain access (regular clothing style must be high too i believe). Lumiose style also gives you access to a bunch of other things, like new hairstyles and discounts to stores and cabs. Here is a list of things that up your style: http://www.serebii.net/xy/lumiosestyle.shtml