Yep, banned from import by US law. Same reg that keeps bbls out. For a few years they let in some receivers and bbls for "replacement or repair" purposes but finally cut out that exception a year or two back.
18 U.S.C. ? 925(d)(3):
(d) The Attorney General shall authorize a firearm or ammunition to be imported or brought into the United States or any possession thereof if the firearm or ammunition -
(3) is of a type that does not fall within the definition of a firearm as defined in section 5845(a) of the Internal Revenue Code of 1986 and is generally recognized as particularly suitable for or readily adaptable to sporting purposes, excluding surplus military firearms, except in any case where the Attorney General has not authorized the importation of the firearm pursuant to this paragraph, it shall be unlawful to import any frame, receiver, or barrel of such firearm which would be prohibited if assembled; or