Backbone of the Wehrmacht - The German K98k Rifle, 1934-1935 by Richard D Law has images of the drawings that are attributed to Walter Schmid. If he's still alive, he would be a good source for copies of the drawings.
From the Acknowledgements page: "Herr Walter Schmid, formerly associated with the Mauser Museum in Oberndorf am Neckar, West Germany, has supplied additional original documents and photographs, and has provided much assistance in the preparation of the edition."
The good news appears to be that the drawings are out there somewhere.
If you get a good copy, post it on this forum.
Regards