John speed writes the following at the end of each chapter of these two models.

Model M: With a little effort a collector should be able to locate a good example of this important Mauser carbine.

The model S: It is not always easy to locate a really good example of the Model S, which is an important piece for any collection.

As a Norwegian I might misunderstand what he means here, but my understanding is that his opinion is that the model S is the harder to find. Do you Americans/Australians/British have another understanding of this text? I have only seen one of these models in real life, so in my opinion they are both rather rare....