(https://i.imgur.com/9KfVNrQ.png)
Pogo has re-released 50 previously-retired Mix-n-Match badges and are on sale for 12 gems each.
To find these badges easier, sort by "On Sale".
This sale is valid through June 10th.
https://www.pogo.com/challenges?filters=MNM%2CON_SALE%2CUNOWNED&sort=RELEASE_DATE_REVERSED