I want to file an O-1 visa application with the help of an U.S. employer. I am a visual artist. Do I need to get an "advisory opinion" to file an O-1 visa application? and how could I get the "advisory opinion"? Thank you.

To file an O-1 visa application, an Advisory Opinion should be be accompanied the O-1 visa application documents. The U.S. employer should consult with an appropriate peer group, labor organization, or management organization in the area of the alien's outstanding ability to get the advisory opinion for the alien beneficiary. Generally, a written advisory opinion should be obtained from the appropriate consulting entity with expertise in the alien beneficiary's field. 

But an advisory opinion may not be required if the petitioner could prove that an appropriate consulting entity does not exist to provide Advisory Opinion. Also, if the petitioner is requesting expeditious handling of the O-1 visa application, an advisory opinion from an appropriate consulting entity may not be submitted with the application documents. The expeditious handling could be granted with regard to O-1 visa application on behalf of an alien who will be employed in the fields of art, entertainment, or athletics.