Is there a complete physical archive of Weekly Shounen Jump (or Shounen Sunday or Shounen Magazine)?
At least, It should be in National Diet Library.

Under Japan's law, all publishers need to submit 1 copy of all of their books and magazines to that library.

Some people succeed to read Jump in there, but it's not a normal library. You may need pre-reservation and require security to enter, but you can search their item from their official website.