Naturalization records after 1906 are available from the Bureau of Citizenship and Immigration Services, as explained in our Research Guide on Naturalization.
The records discussed as part of the Genealogy Program, however, end in 1956. If you were naturalized in the time since, you may be able to request a Replacement Naturalization/Citizenship Document from BCIS. Submit Form N-565 which is available online at www.uscis.gov/n-565.