Each committee or other organization which - (1) represents a State, or a political subdivision thereof, or any group of persons, in dealing with officials of a national political party with respect to matters involving a convention held in such State or political subdivision to nominate a candidate for the office of President or Vice President, or (2) represents a national political party in making arrangements for the convention of such party held to nominate a candidate for the office of President or Vice President, shall, within 60 days following the end of the convention (but not later than 20 days prior to the date on which presidential and vice-presidential electors are chosen), file with the Commission a full and complete financial statement, in such form and detail as it may prescribe, of the sources from which it derived its funds, and the purpose for which such funds were expended.