Gunner
Found In: You begin with this Dressphere.

Thief
Found In: You begin with this Dressphere.

Warrior
Found In: You begin with this Dressphere.

Songstress
Found In: After you defeat Leblanc, Ormo and Logos in the opening sequence

White Mage
Found In: After you finish the mission in Besaid Island in Chapter 1

Black Mage
Found In: After you finish your second mission at Mount Gagazet

Trainer
Found In: Visit Kimhari in Chapters 1 and 2 in Mount Gagazet. When you visit him in Chapter 3, you will start the "stop the Ronso" mission, and receive the Dressphere at the beginning of the mission

Gun Mage
Found In: During Chapter 1, go to Moonflow and talk to Tolbi. He'll ask you to look for his transport caravan along the road leading to the river. Head down and you'll find it close to the crossroads between Djose Temple and Mushroom Rock Road. Start the mission and stay close to him while fighting off all the bandits that try to steal his cargo. If you manage to get him safely to Moonflow, you'll receive the Gun Mage Dressphere.

Alternate Method: If you didn't happen to go to the Moonflow at all in Chapter 1, you can still pick this up during Chapter 2. Once the chapter starts, go to Moonflow and help sell tickets for Tolbi's show. You'll receive the Dressphere for your troubles. You can also gain a powerful accessory called Cat Nip by pushing Tolbi onto the elevator during the start of Chapter 2. This accessory causes all attacks/healing to do 9999 HP instead of their normal value when you have less than half of your life left. This is the only time you can get this accessory, so it's wise to go with the alternative method here.

Dark Knight
Found In: This can be found in Bevelle in Chapter 2 when you are looking for the Vegnagun. Before the fight with Baralai you'll see a chest on an isolated platform. To activate blocks to get there, the key is in the three lifters that allow you to get to the Baralai fight a little before. If the left lifter is up, the right is down, the purple one will go to a different location, and vice versa. Each of these locations has this standing block which then activates the blocks to rise to the path to the chest containing the Dressphere

Lady Luck
Found In: During Chapter 3 visit Luca and you'll immediately be entered into a Sphere Break tournament. Defeat three Sphere Break opponents and you'll be in the finals, where your opponent is none other than Shinra. Defeat Shinra to gain the Gambler Dressphere. You can also gain this Dressphere if you lose to Shinra in the tournament. You can find him with all the other Sphere Break players in Luca, but he'll be much tougher than in the tournament.

Alchemist
Found In: Visit Mushroom Rock Road during Chapter 2 and talk to Clasko. Complete the mission he gives you, and then you'll be able to find him near the save point in that location. Allow him to board your airship. That will unlock a new mission in the Calm Lands. Defeat the boss in the Calm Lands and you'll gain this Dressphere.

Beserker
Found In: Complete the mission in Macalania during Chapter 5.

Samurai
Found In: You'll find this at Kilika Island during Chapter 3.

Mascot
Found In: Get an Episode Complete for all locations to unlock this Dressphere on the Celsius

Machine Maw
Found In: While in Chapter 2, you'll have to find three uniforms in order to enter Leblanc's mansion. One of these uniforms can be found in the Desert. Start the "Oasis Investigation" mission and you'll automatically be transported to an oasis. You can find this Special Dressphere for Rikku here, but you'll have to fight Logos and two henchmen to make it out alive. Defeat them to gain one of the uniforms you're looking for.

Flora Fallal
Found In: While in Chapter 2, you'll have to find three uniforms in order to enter Leblanc's mansion. One of these uniforms can be found near Djose temple. Get to the crossroads where Djose Temple, Mushroom Rock Road and Moonflow meet. The hovers that normally allow you to go from Djose Temple to the Youth League HQ are down, so start walking towards Mushroom Rock Road. Eventually you'll find a sphere on the ground. Grab it to get this Special Dressphere. After obtaining it, you'll have to fight Logos and Ormo in order to gain one of the uniforms you're looking for.

Full Throttle
Found In: Visit Macalania Forest during Chapter 1. Find and talk to Tromell Guado five times in order to gain Paine's Special Dressphere. You can find him in the same place that the first Jecht Sphere is in Final Fantasy X. Another method is to complete the mission in Macalania Woods during Chapter 2.