Pogo has re-released 50 previously-retired Mix-n-Match badges and are on sale for 12 gems each until September 6th, 2022.
To find these badges easier, sort by "On Sale" and look for the badges marked "Re-released".
https://www.pogo.com/challenges?filters=MNM%2CON_SALE%2CUNOWNED&sort=RELEASE_DATE_REVERSED
Must go look! TYVM
Not a single challenge over 300 pogis for me. I'll think about it over the weekend.