TF2 knows about the raw HL2 wav files (at least, the ones in the shared source content), but the soundscape names would have to be included in the primary soundscape manifest for TF2 to know what they are. If you want to use those sounds, you'll need to create your own soundscapes and put them in a file in the tf/scripts directory. The file will need to be named "soundscapes_<exact map name here>.txt" so that the game will read them when it loads your map. You can copy the soundscapes from the HL2 soundscripts, but I would recommend renaming them to something more specific to your map.