I used the advance search in Google to find free resources. Here are a few of my finds:
From Connexions (Rice University)(cnx.org)
Pitch: http://cnx.org/content/m10943/latest/
P2PU.org---this is about rhythm (notes and rests and creating a 4/4 time piece):
https://p2pu.org/nl/groups/music-theory-101/content/rhythm/
And my favorite is Free Music Archive. This site has all genre of music for your listening pleasure (I enjoy classical music): http://freemusicarchive.org/genre/Classical/
