An entire set of the magazines, including the poster, are now at The Museum Of Modern Art, in their Library. They are available to scholars and researchers and the general public by appointment. Here's the LINK to the library.
An entire set of the magazines as well as all the collateral materials - that's the letters, layout boards, mock ups, fliers, and whatever fascinating bits of paper we saved over the years- is now housed at Radcliffe College at The Schlesinger Library. Here's a LINK.