How do you get the Season 2014 - Solo Diamond?
It was a ranked reward. Riot's description in the client reads: “Earned by achieving Diamond in the 2014 ranked season in Solo/Duo.”
Is the Season 2014 - Solo Diamond still available?
No. The Season 2014 - Solo Diamond was a ranked reward. To earn it, you had to reach Diamond in Solo/Duo during Season 4 (2014). Riot does not hand out past ranked rewards again, so you cannot earn this icon anymore.
