Looking for a Lost Half Brother

I have been researching my family and cannot find a half brother. It is very strange almost like he did not exist. His name was David Hannan Wallace, Jr. I don't know when he was born but I know he married a lady named Linda Lou Marnie or Mayberry. I also know he was in the armed forces. I have not been able to find him even though I have found many more family members . If anyone can help I would appreciate it. His father was my father, David Hannan Wallace, Sr. and his mother was Margaret Viola Matthews. He grew up in West Virginia and then moved to Michigan, I think. Thank you.