The wild, original guppy is native to Central America, as well as Trinidad and northern South America. Today, many guppies are found in Asia, especially Singapore, where many fancy strains are bred in large fish farms, and shipped to pet stores all over the world.
http://wiki.answers.com/Q/Where_do_guppies_come_from
i used to think they were from Asia too cuz there's so many over there. when i was in thailand they were just existing in big clay pots and i assume whatever fell in the water. no heaters needed over there