The business manager at most car dealerships will offer you such insurance at the time he's working up your paperwork. There are different kinds of credit insurance - one covers job loss, another covers disability. Remember, the dealer sells this kind of insurance because he makes a HUGE profit on it. I'm not aware of any independent sources of disability insurance.
You'll want to research this some more....
http://www.knowledged.info/go.php?link=insurance
Have a nice day.