Infiltrator Irelia

I am just confused for why I cannot buy this skin. Is it temporarily offline for purchasing for some reason, or is it permanently unavailable? I hate the Irelia default skin(way too much red), but any of her other skins would be much, much better. But my favorite by far is the Infiltrator skin(from looking at the videos of Irelia on YouTube), yet I can't get it in the store. I have tried finding out more information about it, but my searches are coming up with ~2012 price quotes of 975 RP, so I'm very confused since it isn't something that was given away as a promotional item. So why is it not in the store now?

Edit: doing some more searching, http://www.mobafire.com/league-of-legends/skin/irelia-infiltrator-161 at that link I found out the skin was removed December 1st, 2014. Why was this done? It says type Legacy. So, you are meaning it is an old skin and no longer tournament legal? What exactly does legacy mean and is there anyway I can get the skin anymore legally? It looks like that is a no from what I've learned about skins already. It seems strange that you would stop a skin like this, but if it's for balance reasons(maybe the skin is too shady and hard to see the champion?) then I suppose I would understand. If not, then it doesn't really make sense to me.