According to the US. Custom and Border Protection Authority:
“Copies of gold coins are prohibited if not properly marked by the country of issuance. The importation of counterfeit coins is prohibited.
There is no duty on gold coins, medals, or bullion but these items must be declared to a Customs and Border Protection (CBP) Officer. Please note an FINCEN 105 form must be completed at the time of entry for monetary instruments over $10,000. This includes currency, ie. gold coins, valued over $10,000.”