No one will come and offer you a job if they do not already know you are a session musician. The best way to advertise yourself is to start with family or friends. Some who are in the music industry, if they know what you are doing, can help you to come up with the right connections and land yourself a job.
You can also advertise yourself online on sites such as craigslist. Some famous stars have been known to hire video actors and other support from the site.Other ways to advertise yourself online include the use of social media networking to get yourself noticed.