UFO Corki skin

Anyone knows how can i get the UFO Corki skin. i met with my girlfriend in the game. She always want to the UFO Corki skin, i tried to sent her so many mystery skin in order to get the skin. however, it never happen. Now, she wants to break up with me, because she want to get back together With her Ex-boyfriend. i am sad, but i will bless her. i want to send the UFO Corki skin for her as a last gift. how can i get that skin?