The best way to do this is to run into the “sentry” elite on map 1. You will know what the look like because you will see 3 enemies, and they all have a blue core with a pyramid like structure floating above and below said core.
These enemies have two waves of attacks the switch between, the move “bolt” (it is the Green spiral attack that does no damage), and their basic attack dealing 9 damage normally.
The bolt attack gives you two cards, when in your hand cannot be played, but if they stay in your hand at the end of the turn, they get exhausted. It’s as simple as keeping the fight going for a few turns which should happen as you naturally fight them.
If you want to earn this through your own hard work though, I recommend running a shiv deck with the silent character. Shiv decks are decks that help you spawn in multiple shiv’s in one turn, which get exhausted when used. Cards that spawn shiva are:
Cloak and Dagger, infinite blades, Storm of steel, and blade dance.