For the political figures, you may want to check out their personal websites. Not a myspace or facebook or anything like that. Although those sites are rarely, if at all visited by the person him or herself, most politicians usually have some type of an autograph request.
As far as the HOFamers, most of them don't sign ttm. Your best bet would be to see them at a show, although they tend to charge a leg and sometimes an arm. Some of them do sign though. Check the "TTM Addresses" link at the top, or check the address request thread.