I bought this box set when it was first offered by BMG about 10 years ago.  Because it's hard to find this stuff in actual physical media, I encoded all of these into FLAC.  Each album was tagged from freedb.org

Slayer's first recording, Metallica's first, bunches more.  Some of these are available dirt cheap from Metal Blade, I hope you will consider buying them for yourself.  If you're a metalhead and don't know Metal Blade records, you need to educate yourself about one of the most ground-breaking record companies in heavy metal history. 
http://www.metalblade.com/

If you want the real deal, it's available on Amazon, used. 
http://www.amazon.com/Grim-Harvest-Complete-Massacre-Volumes/dp/B0018GBFPY/ref=sr_1_4?ie=UTF8&s=music&qid=1248248904&sr=8-4

If you prefer mp3, here's a link to another torrent: 
https://www.piratebays.to/torrent/3823953/Metal_Massacre_%5BMetal_Blade_Records%5D_-_Volumes_1-11