If your in Freeport, The undead just within the graveyards drop well. I picked up 5 books there last night. Not sure about Qeynos.
I suspect if you hunt in any of the lower level areas with your exp locked you will hit them eventualy. It may be much faster just to buy them though if you can. :) They do use rare componets which your unlikely to have, unless you have the funds to buy the book.
I did manage to get around 2.5 gp for my copies this afternoon so I was fairly happy, was expecting to get around 50 silver.
(Update. I didnt get 5 copies or Ref 4, just 5 different trade books)
Edited, Tue Dec 14 20:44:27 2004 by Corison