Help with AMR Stock, and Sabre stock, please?

My father bought or was given AMR stock in 1971 when he worked for American Airlines, in 1990 we recieved a few Sabre stock certificates in the mail as a dividend, we have no idea what these are worth. A month ago we recieved a letter from Sabre saying the money that was made by its stock was going to be sent to the state of my fathers last residency as lost or forgotten property. I am just wondering what type of value these are worth, I can not find much info on these. If anyone knows how I can find out where my fathers holding account for His AMR stock is located please contact me, or if anyone can tell me how much these stocks could be worth. My father passed away 20 years ago and my mother 1 year ago so we have no info on these things, except for the certificates.