ISO adopted half brother 12/1969 or 1970

Hello, I'm ISO my half brother that was given up for adoptin in Billings (I think) born 12/69 or 12/70...I'm not which one. B/M would be Donna R Accord or Donna R Mosler. She then moved back to Brighton Co. after the birth. I know that a baby was born between my sister who was 1968 and myself 1972. It has been said the baby was a boy. My sister and I have the same father....he was in the Navy when she became pregnant. She went to Montana with her father Don Accord. She doesn't talk about it. Thank You, Robin