Oklahoma Vital Records holds his birth certificate - online application form to fill out & mail in / $15 / pretty speedy service. BUT all birth cert. are NOT open records so you'd have to prove that you're an authorized person (since you are a direct descendant, you should be eligible). There are directions included with the application form and you can call them if you have any further questions - they're helpful.
POTEET ORVAL M Adair 2 13 1912