It generally isn't missing files. It's DB entries for the appropriate npc types and spawn info. Due to the massive amount of work it takes to create such entries, this has generally been done via packet capture from live and then processing that data into the appropriate tables in the DB. There were tools for this but they were out of date enough that they would not even compile. People are working on fixing the tools (see the more recent posts in this thread for more information:
http://www.eqemulator.net/forums/showthread.php?t=20278). Once the tools are working again, anyone who has a live account can help out by capturing information.