Where’s the music folder for the hl2 and hl1 songs?
There isn’t one. The files you are looking for are in the gcf files as soundcache files.
You can use this program to extract soundcache files:
And here is a link to GCFScape so you can find the soundcache files hidden within the GCF’s.
If you’re looking for the sounds’ file paths to use with Wire, try this: http://www.garrysmod.org/downloads/?a=view&id=56174
Or this: http://wiki.garrysmod.com/?title=Half-Life_2_Sound_List