It's called Cheating rewinding! Simply get to the point where you win the duel, win, and if you hate the drop, make the the Doc and turn back the clock.
Now it's important to note, that when you rewind, you now need to pass the turn. Otherwise it will be the same exact drop as last time. Simply pass the turn instead of winning. Rinse and repeat until you find the exact card you need, or until you have to end the game from deck out or some BS card is played and turns the game around.

You're welcome, and happy farming!