You meet them in Chapter Four. I believe you meet the Flower Girl In Limberry (I'm probably wrong though) and you meet Cloud after you retrieve the Cancer Zodiac Stone (once again I'm probably mistaken) from the Steel Giant.

Take the stone back to Mustadio's hometown and a cutscene will happen where Ramza and Mustadio accidentally teleport Cloud to Ivalice from another dimension. Cloud disappears and you have to return to the city where you met the Flower Girl to unlock a scene where Cloud runs into her. Some rogues appear and a battle ensues and Cloud finally joins.

You then need to equip your party with the Move find Item ability and travel to a Volcano themed battlefield. On the top of the volcano in the map is where you'll acquire the Buster Sword which allows Cloud to use his Limit Break ability.

I am most likely wrong but then again I have not played through this game in almost 7 years...