The next time you are at Barnes and Noble or Borders look for a little booklet in the magazine section under Tv and Film publications, it is called:
Call Sheet by Backstage and inside of this booklet is a list of casting directors, agents and talent agencies. This is a good investment for an aspiring model.
It used to be called The Ross Reports, now it is called Call Sheet.
You do however need a compcard or headshot: www.compcards.com to mail to the agencies and casting directors, so do not think an email submission will cut it. Yes email has made the way we communicate change, but for the modeling and entertainment business it is really still a postal mail business and you should get these marketing materials made.