Go to the Archives, then to Characters view character details and costumes. You can purchase the alternate costumes at the Costumes archive for one Armory Key each. Look for the corresponding panel below for the panel location of each character for purchase.
Panel A1 - Aquaman - Regime
Panel A2 - Ares - Regime
Panel A3 - Bane - Regime
Panel A4 - Batman - Insurgency - Arkham City
Panel A5 - Black Adam - Regime
Panel A6 - Catwoman - Regime - Arkham City
Panel B1 - Cyborg - Regime
Panel B2 - Deathstroke - Insurgency
Panel B3 - Doomsday - Regime
Panel B4 - The Flash - Regime - Elseworld - New 52
Panel B5 - Green Arrow - Insurgency
Panel B6 - Green Lantern - Regime - Yellow Lantern
Panel C1 - Harley Quinn - Insurgency
Panel C2 - Hawkgirl - Regime
Panel C3 - The Joker - Insurgency - Arkham City
Panel C4 - Killer Frost - Regime
Panel C5 - Lex Luthor - Insurgency - Kryptonite Suit
Panel C6 - Nightwing - Regime - New 52
Panel D1 - Raven - Regime
Panel D2 - Shazam - Regime - New 52
Panel D3 - Sinestro - Regime
Panel D4 - Solomon Grundy - Regime - Boss Grundy
Panel D5 - Superman - Regime - Godfall
Panel D6 - Wonder Woman - Regime