Earn the indicated amount of points in Campaign mode to purchase the corresponding skin at the "Extras" menu.
Chimera: 2 points.
Dale: 20 points.
Ellis Turner: 30 points.
Graterford: 50 points.
Haven: 50 points.
Humans: 3 points.
Mt. Pleasant: 50 points.
New York: Free points.
Norma: 20 points.
St. Louis: 50 points.
Terraformer: 1 points.
Train: 50 points.
Weapons: 4 points.