The Government has publicized the repatriation of some ancient coins to Bulgaria. But we should be clear about the background of the return. The coins were evidently abandoned after they were seized based on alleged misstatements on a customs form. Though Bulgaria has sought a MOU with the United States, US import controls have not yet been promulgated. Moreover, there is no allegation the coins in question were "stolen" from Bulgaria. Indeed, that would be a difficult case to make given Bulgaria's open and legal trade in the exact same items.
For more about the issues surrounding the MOU that is being considered see here.