While it is not clear why you would need this, Customs and Border Patrol own requirements for how long you, and it, needs to retain such a record is 5 years. While your receipt may no longer be in CBP records, you could still make a Freedom of Information Request, just in case.
Requirements for keeping CBP records and entry documents on file
How long are importers, carriers, exporters, travelers and brokers required to keep U.S. Customs and Border Protection records and entry documents on file?
Importers, exporters, carriers, and brokers are required to keep their U.S. Customs and Border Protection (CBP) records and entry documents for five years from date of entry, or five years from the date of the activity that required the maintenance of the records. However, travelers who physically clear CBP by making an oral declaration are not required to maintain supporting documents, as long as they are not declaring commercial merchandise.
For additional information on the requirements for maintaining CBP records, please refer to 19 CFR § 163.4.
What Records can CBP Provide under FOIA?
Records Regarding My Inspection or Examination upon My Arrival at a U.S. Port of Entry
Concerns about how you were treated by CBP officers, or if you have a general or specific question(s) about CBP or your CBP inspection:
CBP Info Center
or call (877) CBP-5511 (227-5511) for U.S. Callers or (202) 325-8000 for International callers