Fist makes holsters for both the M and the S series (Although the S series isn't yet listed, they do infact make them, I have one on the way)
Highnoon makes them for the M series, I bought a Mr. Softy and it's working fine and dandy for my S40.
The Holster that Steyr sells is for both the M and S series, In reality the S series is only .42 inches shorter in barrel length than the M series, so using any holster made for the M series for an S series isn't going to add much to the Holster.