Write a letter to a management firm

I am struggeling to write a letter to a management firm which I have been wanting to ask if they would be interested in managing me as a singer. This firm is calles Reigndeer Entertainment, but I don't know who to address and how to formulate my letter in order to make clear what I am looking for. I will be including pictures and a demo cd in the letter.
I have been singing for many years and am looking for representation. I am currently with a replacement agency in California, but they are specialized on acting and modeling an cannot really help me with what I am trying to accomplish. I am basically looking for a record deal.
I have experience with public performances and will include a resume also. It would be great if someone could help me figure this out. I am basically looking for a management and representation who can help me achieve my musical goals.