Dear Rei Kokkonen,
Thank you for posting your question to history hub.
The Federal Government does not ordinarily create or maintain birth, adoption, death, marriage or divorce records. Such records are made and kept by State and local governments rather than the National Archives. We suggest searching substitute record sources such as probate records, church records, and newspaper records that may uncover more information about your ancestor. A precursory search of the NARA Catalog and Ancestry.com yielded no definitive results on Amanda, other than a "New York Extracted Marriage Index (1866-1937) that shared a certificate number with a William Kokkonen. That Certificate Number is 12584. If you have any more information, even a middle name or initial, feel free to post a follow-up.
We hope this information was helpful. Best of luck with your research!