I just wanna ask about the championship riven

I only play riven and the best skin is championship riven. i watched the challengers play riven everyday how can they get championship riven but new player cannot have it? i played dis game from the end of s3 i cannot have lots of skins but you know for a riven new player although we have good skills and other 4 skins but the only one CS Riven we cannot have any chances to get it Its really sad. Riot put the CS thresh in the store but why we cannot have CS riven in the store? its a game we want to get the skin for it looks pretty but now? I think dis is the biggest problem to balance on the game for our new players! serious, lost of new player asked why boxbox can have a korean Name in the game? why we cannot have it?