This post is for finding all the dresspheres during the game, for those people who have some difficulty in finding them:

Warrior: present from the beginning of the game

Thief: present from the beginning of the game

Songstress: present from the beginning of the game

Gunner: present from the beginning of the game

Black mage: complete the mission 'outrun the leblanc syndicate', and
then view the 'Gagazet Sphere'

White mage: complete the mission 'where's wakka' on besaid island in chapter 1

Gun mage: either complete 'Guard the Hypello' mission on the Moonflow in chapter 1, or sell at least six tickets in the mission 'Sell those Tickets', also on the Moonflow, but in chapter 2

Alchemist: complete the mission 'Clean Sweep' on the Calm lands either in chapters 2 or 3

Dark knight: check here for a thread on getting this

Berserker: complete the mission 'Secure the Agency' in macalania in chapter 3

Lady luck: either win the sphere break tournament in luca in chapter 3, or beat shinra in luca in chapter 5

Samurai: either find on the floor in kilika temple during 'Pest control' in chapter 3, or find in a chest in the same place during chapter 5

Trainer: recieve from Kimahri in chapter 3 if you say "you have to learn to deal with these things" and "you have to figure this out on your own" . Alternativly, talk to him three or more times.

Mascot: get 'episode complete' for all missions during chapter 5

Floral Fallal: you get this automatically during the mission 'Two birds, one stone' on the djose highroad in chapter 2

Machina Maw: you get this automatically during the mission 'Water we doing here?' in Bikanel desert in chapter 2

Full Throttle: recieve this by speaking to Tromell in Macalania woods during chapters 1 or 2