ok, when looking through the neopets forums, some users have noticed a pattern. Some of the common places to find the books are in rooms 3,3; 6,6; 9,9; 12,12; 15,15; 18,18; 21,21; 6,21; 12,15; 9,12; 18,15; and 9;15 (where i personally found mine).... the numbers refer to the ones in the url after the 'arc': 3&arcx=9&arcy=15&rea

the url up to that point is (not the full url):

ttp://www.neopets.com/altador/archives.phtml?goarch=01e87d2ec7fb94fcaf392711dd5a1f13&arcx=9&arcy=15&rea