The Froggy Armor is the reward for completing the Potential Princess Sightings quest. Traysi, the quest giver, will award you pieces of the set as you finish the 12 quests. You receive the Froggy Sleeve after 4, the Leggings after 9, and the hood at the end. You have to visit Traysi at the Lucky Clover Gazette HQ to get it.