You can obtain a Certificate of Non-Impediment (Nulla Osta) from any U.S. Embassy or Consulate that provides consular services. These facilities are typically located in major cities throughout the United States. Some of the main cities where you can find U.S. Embassies or Consulates include:


  1. Washington, D.C. (U.S. Department of State)
  2. New York City, New York
  3. Los Angeles, California
  4. Chicago, Illinois
  5. Miami, Florida
  6. Houston, Texas
  7. San Francisco, California
  8. Boston, Massachusetts
  9. Atlanta, Georgia
  10. Seattle, Washington


You can visit the website of the U.S. Department of State to find the nearest U.S. Embassy or Consulate to your location and to learn more about their services, including obtaining certificates for marriage abroad. Additionally, it's advisable to contact the specific Embassy or Consulate directly to inquire about their procedures for obtaining the Certificate of Non-Impediment and to schedule an appointment if necessary.


Source:

https://www.italiandualcitizenship.net/italian-consulate-locations/