www.archive.org has worked for me in general. search usfirst.org and go through the pages. The only years I haven't found information for were 1992-1995 and 2001 (1992-1995 can be found on FIRSTwiki, as Joe Ross stated).
I'm interested in finding the 'exact' white papers for the 2001 game, because this one strikes me as the most unique out of all the FIRST games.
_Alex