^ There is no "spot" to get cards at a regular pace (besides Outlaw's post) - I have found that higher enemy players carry better cards (I'm actually holdsing 68 cards at the moment, including a Royal Flush in hearts and diamonds - A, K, Q, J 10, and several other A's, K's and Q's). So a Cadet may give a 2 of diamonds, a Vet may give an 8 of spades or even a 10, but my best cards have come from really high enemies like Stumps (got my Aces from these guys), Padres Beach (The Gyps and Raiders have given me Kings / Queens) and anyone at Tormenta (have gotten several A, K, Q, and J here) - that, and flagships - for some reason I tend to get good mid-level cards on boarding boats (anywhere from 8 to J's).
And thats all I got...