You can start with the works of Emmerich de Vattel on the Law of Nations, referenced frequently by the founding fathers, and in whose work the phrase “natural born citizen” is actually found.
https://nobarack08.wordpress.com/2009/11/30/vattels-law-of-nations-and-the-founding-fathers/
And we can also go to Blackstone's Commentaries, also well known to the Founding Fathers, and find an entirely different definition of natural-born citizen.