Dear Ms. Diehn,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located a series titled Orders, 7/7/1835-3/5/1953 in the Records of the Post Office Department (Record Group 28). The records are not yet digitized and available in the Catalog. For access to and/or copies, please contact the National Archives at Washington - Textual Reference (RDT1) via email at firstname.lastname@example.org.
Also, you may wish to search the Smithsonian’s National Postal Museum; 24 Rural Route Addresses or How to Find a Physical Address for a Rural Route for additional information about the change to 3-digit addresses in Big Bend, Wisconsin in 1952.
We hope this is helpful. Best of luck with your research!