Contact the music publisher whose song you want to redistribute. The original music publisher owns the rights to the songs and they will be able to grant you a mechanical license to reproduce the music. You will need to indicate to them how many copies of the song you will reproduce so the publisher knows how much you will have to pay to cover the royalty fees.
Contact a licensing agent who will do the work for you. Many redistributors choose to use a licensing agent, such as the Harry Fox Agency, Broadcast Music Inc. or the American Society of Composers, Authors and Publishers. Fill out a form and indicate what song or songs you want to redistribute. The licensing company will contact the music publisher on your behalf and arrange for a mechanical license.
Obtain a compulsory license so that you might redistribute the music. This process is quite complex and is the last resort you should take to get a redistribution license. Compulsory licenses are very work intensive. Even after the compulsory license has been obtained, there is ongoing administration and reporting.