I would contact the State Guard which ever state you reside in. They have resources available. For this for my dad awhile back.
Dear Mr. Mcquade,
Thank you for posting your request on History Hub!
For access to personnel records of non-active duty Army National Guard enlisted personnel and officers, please contact the Adjutant General of the appropriate state using the addresses listed on the National Guard website at https://www.ngaus.org/states-territories/state-association-directory.
We hope this information is helpful.