said that you only need a bonus of 100% to unlock. Makes sense since it's an additional 100, so really it is 200% of the score.
You will need to equip cards to your Expedition replay on Score Attack. You can equip up to 5 cards during this game type and just make sure all of them add up to over 200%. It's fairly easy to get good cards if you purchase the Challenge Pack from the marketplace for 20,000 credits. With the cards equipped, simply beat any level and this should unlock, regardless of your score.
NOTE: This is the best way to go for the golds as well. Good Luck!