Dictations for practice are available at http://www.4shared.com/dir/9434129/90fe7...aring.html. However, there are no keys posted yet.
You can post your transcripts there for some senior QA to verify.

Do not ever be taken in or dream of becoming a home-based medical transcriber fresh after training. At least not until you have had 2-3 years full-time office-based experience in multispecialties.