Where to buy PMSM motors?
When brushless, synchronous 'DC' motors were first introduced the stator windings were wound in two different ways: (1) such that the generated emf, or equivalently torque coupling to the rotor appeared as a trapezoidal function and (2) such that the generated emf, or equivalently torque coupling to the rotor appeared as a sinusoidal function. The motors wound in the fashion of (1) acquired the name 'Brushless DC Motor' and the motors wound according to (2) were called 'Permanent Magnet Synchronous Motors' (PMSM). But the fact is that both types of winding's are technically PMSM's. The trapezoidal wound motors I believe then were less expensive to manufacture, but my understanding is that most if not all PMSM's today are sinusoidally wound.

A sinusoidally wound motor that is sinusoidally commutated will offer the least amount of torque ripple as the motor rotates, so this introduces less jitter in rotational movement as compared with a motor that is trapezoidally commutated - using Hall sensors. But commutation either requires an encoder signal for the commutation or the smarts of sensorless commutation. If you are doing position control you'll need an encoder regardless. But your amplifier needs to support encoder input.