Where can I find old midwife birth records? Or tribal birth records?

Looking for birth records on my paternal grandfather.  I've taken a DNA test  and it matches me to a 3rd and 4th grandfather.  The problem I've ran into is I can't connect him to a father or mother even with this information.

Bert Roy, Oklahoma, DOB: 10.18.1891 Every record that I have found on him does not include parents.  This including the military records it says parents unknown death certificate parents unknown.  I knew all of his children and he is my mother s father.