I had 19 pages after tower of babil and could not find the last one, i had already started the tour of all places to find the last one, then found this topic and sometimes checked some places again to be sure. Nothing, so i started again the tour of the places i had not checked yet.
In the end i found the last one in Auslen Cave, entering from the north, in the screen after the one with the levers, just before the stairs going down there's a secret passage going right. It seems i missed it the first time i passed through.