http://www.ifixit.com/Answers/View/115954/does+the+home+button+comes+with+the+digitizer
So after some more investigating it seems that you are going to have to buy a new digitizer assembly as the home button assembly and flex cable are combined inside.
Other than that I have found ZERO accounts of anyone selling the flex cable separately and I could find no mention of it being anywhere other than attached to the digitizer.
Good luck! Hope this answer helps lol.