To use them you need to complete the garment grid, you change spheres by pressing L1 and then you after you have passed all the spheres on the grid you will be able to use the special dresssphere.
Floral Fallal (Chapter 2):
When you're doing a hunt for Syndicate uniforms, go to Djose Highroad. A mission will start - go along the road and you'll spot this special dresssphere just lying there, waiting for you to be picked up. Full Throttle (Chapter 1 and 2):
Chapter 1 - Go to Macalania. There are two screens inside here which are labeled as 'Macalania - Spring'. Anyway, look for X-shaped cross on your mini-map (you've just found screen 'Macalania Woods - Lake Road'). NE exit leads to the 'Macalania - Spring' screen you need. You'll find Tromell here. Talk to him four times and he gives you this special dresssphere. Chapter 2 - Go to Macalania. Look for X-shaped cross on your mini-map (you've just found screen 'Macalania Woods - Lake Road'). NE exit leads to the 'Macalania - Spring' screen you need. You'll find Bayra here (bird with harp). Talk to him and complete 'Track down the troupe' subquest. When you're asked if you wish to board Celsius, choose whatever. If you choose [No.], you'll see Tromell emerge from the woods. Speak with him four times and this special dresssphere is yours. If you choose [Yes.], simply go back down to same screen again, find Tromell etc.
Machina Maw (Chapter 2):
When you're doing a hunt for Syndicate uniforms, go to Bikanel - you also need Letter of Introduction key item, which you get from Gippal in Djose temple. Talk to Nhadala and she'll ask you to go investigate strange events in Oasis. Talk to the pilot of the hover and pick Oasis. Mission will start. Simply approach the oasis and you'll spot this special dresssphere just lying there, waiting for you to be picked up.