Oi! This might be a repost, but for those who doesn't know about it, here's how you get both midsummer tabards.
(You can normally only get one)
1. If you havn't already got a tabard yet, queue up for Frost Lord Ahune and get the quest item after you killed him and get the tabard.
2. Go to void storage and place your tabard in there
3. Go to the Tabard vendor and click "I've lost my Tabard of Summer X" (obviously click the one who don't have)
There you go! Now you have both tabards!
https://i.imgur.com/ZpH8RKf.png