As IRstuff has stated, the spindle motors used in disk drives are intended to accelerate a mainly inertial load in a short amount of time and continue as a velocity servo. The motors could conceivably be used in a robotic (very small robot) application. Sensorless should not be a concern, because you will have to provide some sort of shaft position feedback for position/speed servo control. Although the motors are mass produced ie. relatively inexpensive, they have been designed in to the drive and you may find difficulty in getting them on your own. And if you do, they will probably consist of a part set rather than a complet motor. Their are several "small motor" companies that provide quality products at a reasonable (in quantity) price.