The APO chapter at UofA might have some historical information, but the chapter history probably has gaps. According to
http://www.uark.edu/~alphiom/about_history.php , the APO chapter was active from 1932 to the late 1970s, it rechartered in 1980 and then dropped to nonexistant in the late 1980s and just barely (down to 0 at one point) avoided going inactive again around 1989. So I'm not sure how much of their pre 1990 history they have, but if they have it, especially in the 1960s and 1970s, it probably will include info on Gamma Sigma Sigma.