Cactuar and Tonberry
To get these summons you must go to certain missions and find them.
Go to the third mission in the first file of the Genesis Missions and pass the boss and head through the path next to him to see a cactuar. Fight it and their missions are unlocked.
Go to the fifth Mission in the first file of the Seeking Prescious Items missions. Head to the east path instead of the west path where you find a bomb. Going to the east path will soon lead you to a Tonberry fight it and their missions are unlocked.
Added by: Darkrai X Apr 6th 2010, ID#3332