The Shiny Charm (note, not Shining Charm. ;3) is a key item in Unova that can only be received by completing the National Pokedex (excluding event legendary Pokemon) and showing it to Cedric Juniper in the Juniper lab.
It increases your chances rapidly from 1 in 8,192 to 1 in 2,731. If the Masuda Method is applied, it goes to 1 in 1,024.
Hope I helped. :)