Dieter Marschall's book might have what you are looking for.
Need to know what model and caliber.
Walthers were made in 2 different locations in Germany, and in France. we need to know the model of your "Walther gun".
send me the serial number and I might be able to tell you when it was made..............
You will need to contact Walther to find out.
Walther
No such model made by Walther
There are serial number tables that have been published.
1931 to date
Impossible to answer withou a serial number and DETAILED DESCRIPTION of all markings.
See Related links below Made about 1935
Germany. 1970's or so
Your question does not include if there are any german military markings associated with this P-38 pistol.That being said and the high serial number,I would assume that it was made after 1945.It could be made by Walther any time there after.You may want to contact Walther directly and see if their customer service dept may be of some help.