In order to find surviving IMITATION OF LIFE cast members, I would suggest
two sources--the Screen Actor's Guild and/or the American Federation of
Radio and Television Actors.  Both of these unions have membership offices
that may be able to help.
 
Good Luck,
 
David Ezell
 
David Ezell
Georgia Institute of Technology
Atlanta, Georgia
 
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Online resources for film/TV studies may be found at ScreenSite
http://www.tcf.ua.edu/screensite