The rifle was made in 1918, and the Royal Rifle Factory at Erfurt was closed after WWI, so the rifle was not made as a K98k, although it might have been converted to the K98k configuration sometime before or during WWII.
Stocks are available from time to time for the Model 98 Mauser, but most of the military ones are for the K98k and may or may not fit your conversion.
Original stocks are, for practical purposes, non-existent.
You might try a Google search on "Mauser stocks" and see what comes up. Also check your local gun shops, as they often still have stocks that were taken off in "sporterizing"; you won't find an original stock, but you might find something close. Since the rifle has been "sporterized", you will also need the front band and maybe some other hardware.
Jim
