You will be able to purchase these cards in the Store on Rewards / Faction tab after minimum Reputation is achieved to unlock the reward. Every faction does have an associated achievement to play all reward cards on a fixed mission and receive gold in reward. Most of the time player will get more gold back than amount spent to buy one copy of each of required cards. However, note that this is an one-time proposal only - 2nd and next cards will not get any refund.
Trying to grind mission with highest reputation per energy gain is not always the best and the fastest way to raise reputation due to increased chance to lose. Most of the time it's better to step 1-2 missions back and grind there.
Reputation after completing all associated missions (once each): 814 / 2,000 (1,186 to max).
RPE - reputation per 1 energy spent, GPE - gold per 1 energy spent.