These have been out since September, but I didn't see anything about them when I searched and I just found them yesterday, so I thought that I would pass it along.
http://www.amazon.com/Thrash-Metal-Metalhit-Free-Download/dp/B0042NDKIA/ref=pd_sim_dmusic_a_3
If you look in the "Customers who bought this, also bought..." section, there are a bunch of others.