Your question is an obvious one for the uninitiated Pound freak.
 
Start at Yale.
http://www.library.yale.edu/beinecke/
 
thats the mother lode. But then check Ransom Library at the University of
Texas--Austin. Then Lilly Library at the University of Indiana. Other much
smaller collections at University of Pennsylvania, Hamilton College and
Harvard.
 
Cam McWhirter