Weekly Variety publishes lists of film bureaus about once a year.  Sorry
I can't be more precise.  You might try the bibliographic service called
Magazine Index which indexes Variety along with other periodicals.
 
There are other bibliographic sources that university librarians might
know of.
 
Cal Pryluck, Radio-Television-Film, Temple University, Philadelphia
<[log in to unmask]>  <PRYLUCK@TEMPLEVM>