I am on the search for a motor out of an E39 M5. Would any of you know of a good place to search for such a beast?

The wife has given me permission to buy a motor and a stand so I can teach my son about engines and how to work on them. I don't care if it is not running as I would prefer to tear down and rebuild. As long as the block is solid and the major parts are okay I am happy.

Thanks in advance.