Team Plasma's Colress may have run into some bad luck against you before, but he's trained his Pokemon substantially and now waits for you in the Plasma Frigate, docked next to the P2 Lab. It's quite a jaunt heading over there, though!
Colress can be found in the control room, where he was found in your previous trip to the Plasma Frigate where you battled him.
||PKMN Trainer Colress||$14800|
After beating him, he'll bestow upon you a Master Ball! Yes, that's right, a second Master Ball in the game. Excellent!
You can battle him again once per day, but he'll be found on the front of the deck of the ship in any future battles. And no, he won't give you any more Master Balls after the first.