So.... when is Blue Essence going to be sold in the store?

I've seen Riot mention something about it in the past to slightly pull out the RNG aspect of Mastery levels 6 & 7 (hoping you get a champion you don't want from the chests you get for whatever reason in order to turn it into blues). I just got the two mastery 6 tokens for my other two most played champions~ (my other one, Jhin, was already at 6).