I'm a non US citizen who will be in Atlanta during a layover and I'd like to buy a MacBook Pro with some upgraded specs. Is there a way to be sure that the exact MacBook will be available at the store?

Yes be the first there and ask go at 8am

Yes make sure to be there early in the morning 8 a.m. upstairs stand in front of the store and they come out and ask you what are you here for and let them know. Try to be the first 5 because it get busy.

More than likely