First you need to get an Epic Card. These can be collected from chests, or finishing a level on the solo quest.
The first Epic Item
I discovered is on the harbor side of the Backyard Battleground (to your right if you are coming from the plants side, left if the zombie). Near the boat that has been dry docked on the harbor side, there is a trash heap that needs to be cleaned for 5 stars.
(Stars can be obtained by completing quest board challenges. These are the same stars that are used to open chests.)
This will allow you to
and give you the achievement.