Chocobo

They are found in many places. The only two I can think of are the ones that is in the northeast mosphoran highwaste, and the one in the south area of the phon coast. They will be walking around, and appear as a green dot on your map.

First make sure you have some Gyashal greens, Then feed them. That's the only way to ride them. You can buy gyashal greens from almost every shop that carries items. If the gyashal greens don't work then something is wrong with your game.

Hope this hepls.

Yeah you can but there arent many of them. If I remember rightly there are 2 you can ride. One in the Mosphore Highway and one in The Phon coast. You'll know if it is a wild one that can be ridden because it will have a speech bubble over it's head. And remember if you can ride on a wild chocobo it means there are secret passages that are only accessible on a chocobo. Like you said you need ghyashl greens to mount them. Have fun!

There are chocobos you can ride for free if you give them gysahl greens but these chocobos are not the wild ones that you fight at all these are the regular chocobos that you normally have to pay for you will just see them on there own in certain areas and if you have gysahl greens and you talk to the chocobo an option to give them to the chocobo will come up then you will be able to ride the chocobo. I have only found one of these chocobos and that is in the Mosphoran Highwaste where you do the side quest for the Esper Exodus.

I don't think that you can ride chocobos for free
Im not sure

You find them wandering about in places. They've lost their riders and you don't have to pay, but you still have a time limit.