How can I calculate DC motor continuous current?
Motor current is dependant on torque and voltage on speed (loosly), They don't tell you current because they don't know how much torque you will need. 

Your calculation is roughly correct and if you get a driver that can source/sink 22.9A + a safety factor (10-20% for hobbiest use IMO) you will be safe. If you are a building one of these for your own use and you know not to over torque the motor then you could get a way with less. 

For production you should probably get one that supports far more current (50A is the lowest I would use for this motor).