It's not the freehub assembly which is available. It's the ratchet on the motor side that the freehub pawls engage. It's a pressfit part on the hub side. The image from a Go Swissdrive video but it looks very similar on the Specialized motor. Specialized doesn't seem to list any of the motor internals as available parts such as axles, bearings and etc.
My commute has a fair number of starts and stops due to lights and stop signs. Since the Turbo S is a speed pedelec I'm a little more cautious to appear to follow the "rules". Even so I am a little surprised they wore out. I use the same input as if I am riding my road bike. I have a Stages left side power meter and I usually average about 200 watts for the ride. (The Stages FSA mega exo crank was a closeout.)