MarioMania:
We look-up old TV listings in newspapers or vintage issues of TV Guide that we may own or borrow and get listings we post on this board that way.
Another way I get old Boston (my hometown) TV listings: At my local library, I can access through one of their "catalog and database" computers TV listings in every issue of the Boston Globe from June 9th, 1948 (the beginning of commercial TV broadcasting in Boston) through 1981, with the exception of a couple of weeks in the early Spring of 1966 when the Globe and the other Boston papers didn't publish due to a labor strike. This is from a service called Pro Quest.
You may find it possible to access old newspapers in your city (including vintage TV listings) in a similar fashion.