You can also download products form aa.com, such as the monthly PDF schedule, that show the miles.

NONE of these will be spot-on accurate - even American changes the miles between city pairs with some degree of frequency, though they will all generally be within a very few miles of each other.

You can also download spreadsheets for AA frequent flyers that have mileage tables (you would need to modify the city pair table to include newer flights or significant change sin AA's miles awarded, but it's fairly easy.)

These and many more tools will be found linked to in the Unofficial Users' Guide sticky thread; look in the part entitled "Travel Weather, Mappers, Times and Related."