Follow this step to get Chocobo in ff13:
-do Mission 3 at central expanse to unlock mission 5 and 7.
-do Mission 5 and 7 at yaschas massif to unlock mission 12.
-do Mission 12 at arid strath to unlock mission 13.
-do Mission 13 at central expanse to unlock mission 14.
-do Mission 14 at western benchland to get chocobo.
Now you can ride chocobo after completed mission 14.
Phuoctot rock, good luck and have fun.