Tentman,

Live is sometimes not so complicated as it seems.

Every stockmaker , who has the pattern for the standard length 98 can easily do one for the intermediate length Mauser.

You can take any standard 98 riflestock if you can live with a slight missing wood as is shown in the picture.
The picture shows an intermediate action in a standard 98 stock.

http://img824.imageshack.us/img824/7192/perukopie.jpg