I think there are three chocographs in the air garden.

Have you been back to the forest with your mountain chocobo? ...probably so.

Anyway, like endless said, pay attention to the Mene about "you've found all the chocographs here."

And, in case it will help, here are the chgrphs. that increase your abilities:

As they are listed in your inventory

4) healing shore
12) dawn lagoon
14) green plains
20) mist ocean

Of special interest is "mist ocean," which gives you the ability to fly. It can't be obtained until after you get the airship (for story reasons). That might be why you haven't found any chcgrphs. lately.

You can't get to the flying ability, until after you get the airship.