Does anyone know where name GRAHAM came from, in Alexander Graham Bell's name? Someone said that it came from his grandfather, but I cannot locate this information.

Check the links at the bottom of this page. There is much about the genealogy of AGB on the net too, including at the Library of Congress site online.

Look through this Google page on Alexander Graham Bell:
alexander graham bell+genealogy - Google Search

Edit: This from Wikpedia - "At age ten, he made a plea to his father to have a middle name like his two brothers.[12] For his 11th birthday, his father acquiesced and allowed him to adopt the middle name "Graham" chosen out of admiration for Alexander Graham, a Canadian being treated by his father and boarder who had become a family friend.[13] To close relatives and friends he remained "Aleck" which his father continued to call him into later life.[14]"
Full article here - Alexander Graham Bell - Wikipedia, the free encyclopedia