Dear Mr. Singerton,
Thank you for posting your request on History Hub!
We searched the National Archives catalog and located the series Letters Received, 1789 - 1906 in the General Records of the Department of State that includes in the file unit titled January THRU March 1794 a Letter from John Jacob Ulrich Rivardi to President George Washington. For more information about these non-digitized records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at firstname.lastname@example.org.
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For more information on Rivardi, you may be interested in the War Department papers regarding Rivardi. Papers of the War Department is a project of the Roy Rosenzweig Center for History and New Media at the George Mason University
Records of his death would most likely be in the custody of the The Martinique Archives and they may be able to direct you to resources for local historic newspapers of the islands that contain relevant information.
We hope this is helpful. Best of luck with your research!