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.