For the 360 version, you have to win certain tournaments to unlock all the classic players - you're told how many players you can unlock for each tournament, but not who they are.
To include them in the ML, select "yes" at the opening settings and they appear during the very first transfer window. Even better, you can sign them for free (only offer wages). After that transfer window, however, you have to pay cash as well as wages to sign them.