I believe they are located within the main.pack file under the "data" folder in your game's directory. In any case it's in some pack file. You'll need an extractor to access it. You can get one at the link below:
Link
I have not used it myself yet, but if it follows in the tradition of the previous games extraced files will be read before the ones in the .pack files. If not I believe this utility can also repack it, but make sure you back it up first.
thank you for the link