Hello, I'm in same problem, i bought a motor with the same caracteristics and a motor : 3.2V an 2.8A. Can i control it with the motor shield (3* SN754410 in Piggy Back ?) or i have to create other h-bridge ?
At that point you are essentially building your own H-bridge. If you want to go that route, there are a lot of resources on the web with H-bridge circuit designs. If you prefer something off-the-shelf, Pololu has a nice range of moduler stepper controllers.
Another approach is to just use a different motor. A low voltage motor like that (3.2v) needs high current to develop torque. If you double the voltage, you can get the same torque with half the current. An 18v motor with a 0.5A/phase rating should have similar torque and will comfortably run on an un-modified shield.