U.S. National Archives (Record Group 104, Entry 2, Boulton Correspondence) Publique Deposited
National Archives entry description: "Chiefly letters from and drafts of replies to Matthew R. Boulton of the Boulton Mint, a private institution in England, which supplied the United States Mint with copper. The letters dated after 1808 are signed "M. Robinson Boulton." Included are a letter of January 1, 1843, from the agent of the Soho Mint (the Boulton Mint) to the Director of the Philadelphia Mint relating to mint operations after the death of Mr. Boulton, and a report of May 15, 1836, from the Philadelphia assayers regarding the use of silver tokens for currency and referring to the Boulton Mint."
This material was scanned in Philadelphia under the direction of R.W. Julian, operating via a grant from the Central States Numismatic Society.
National Archives catalog record: https://catalog.archives.gov/id/561213. See also the National Archives & Records Administration numismatic finding aids at https://nnp.wustl.edu/library/archivedetail/538870.