The below link has the download for the embedded JBoss EJB3 container.
http://sourceforge.net/project/showfiles.php?group_id=22866&package_id=132063&release_id=346762
But the release is from back in 2005. Since this release, there are some bug fixes such as
http://opensource.atlassian.com/projects/hibernate/browse/EJB-46
Is there any chance that a new version of the embedded EJB3 container will be released sometime soon.