That depends, are you talking about the shooting script, the released-version's cutting continuity, or the cutting continuity of Welles' original cut?
Shooting script? I'm not sure. Released cutting continuity? I'm sure a search with google should turn up something. Original cutting continuity? Only one source, The Magnificent Ambersons - A Reconstruction by Robert Carringer. Out of print, but a great book if you can find it (check out your library).