I'm working on some building and settlement designs for Middle Earth Total War and currently have hit a small snag

In RTW creating a new item entry was relatively easy using vercingetorix db_edit but that doesn't work for BI - you get a runtime error.

Therefore for BI you have to edit the decompiled descr_items.txt and then from that the game creates the item database. The problem is that the original cas files and accompanying resources aren't in the release of BI and so when I recompile the descr_items.db it no longer has the walls and original buildings just my added buildings.

Does anyone know a fix for this, another db editor or has a link to the original model files that I can use?