Saw a post instructing how to get those two skins, but I was unable to get them. Riot Girl Tristana is not in the side bar, and Dreadknight Garen is not received, even though I am following LoL on twitter.
Follow those easy step for those skin, and unchained alistar ! https://boards.na.leagueoflegends.com/en/c/general-discussion/5szExW25-dreadknight-garen-skin-redeeming-tutorial
they're available
did you check https://support.riotgames.com/hc/en-us/articles/202083184-Promotional-Content-Free-Swag- ?
I believe you can contact support and they will give them to you.
