There are 3 Class Masters. One in each major city of Kaslow, Ilia, and Jale.
Kaslow- When you enter the portal to the city, turn left, and he is right next to the wall.
Ilia- This one is a little more difficult. He's around the same vicinity as the bank tellers. Coordinates: X:346, Y:219
Jale- Once you enter the portal into the city, go down the 1st flight of stairs, and turn left.