How do you get the Season 2014 - 3v3 Challenger 3?
It was a ranked reward. Riot's description in the client reads: “Earned by achieving Challenger 3 in the 2014 ranked season in 3v3.”
Is the Season 2014 - 3v3 Challenger 3 still available?
No. The Season 2014 - 3v3 Challenger 3 was a ranked reward: to get it you had to reach Challenger in Twisted Treeline 3v3 during Season 4 (2014). Riot does not give out past ranked rewards again, so it cannot be earned anymore.
Season 2014 - 3v3 Challenger 3 is one of the rarest LoL summoner icons.
