An expansion is an expansion of the game!
You can search for expansion in the net or build your own expansion and save it to your
[DFX1 Path]\expansion\[EXPANSION FOLDER NAME]\[EXPANSION FILE NAME].PFF . Remember, the expansion file must have the same name as the folder where you saved your expansion.
by the way, try this mod:
http://www.novahq.net/forum/showthread.php?t=45720
is not an expansion so it requires you make a copy of your DFX1 folder..