I found his obituary on legacy.com but couldn't read the whole thing because you have to pay for it.
I think you have standing to request his "vital records" from the county seat where she was born. Is he on your birth certificate? Do you believe he signed hers? If so, it sounds like you can walk in there and request a copy of any birth certificate your father signed.
https://www.lavote.net/home/records/...a-birth-record