Hey, sorry for the late reply! I've been in a little situation lately and it's been killing me. Anyway, try restarting your game and it should load all of the sound files in your Garry's Mod game. Remember to copy down the exact !command off the list. So far I think one is missing, but if more audio files are missing since, then that would really suck. I just recommend rebooting the game or re-installing the addon (then reloading).

I also seized development and no longer have the files. Sorry!