For some unknown reasons, Datus C. Smith, Jr. the former director of the program, distributed the archival documents in three places in the US. First, the Library of Congress holds the “Franklin Book Program Collection: Archival set of Franklin Program publications of American books translated into Middle Eastern and Asian languages” (no link as yet). Second, the Princeton University Library holds the “Franklin Book Programs Records” available at the Department of Rare Books and Special Collections (FRP). Third, the Harry Ransom Center in Austin, TX holds “Franklin Book Program Collection, 1952-1978” (FHR) (a preliminary link is provided recently, update Sep. 2020).
So far, I have visited the FHR twice in 2011 and 2015 (about 6000 pages of the documents were photographed). I also visited the FRP in March 2017 for two days and made copies out of 1000 pages.