[Corpora-List] Zipf's papers on the web?

[chkim at etri.re.kr]

Hello.

I am looking for some papers :

  GK Zipf, Selective Studies and the Principle of Relative Frequency in
Language (?, 1932)
  GK Zipf, Psycho-Biology of Languages (Houghton-Mifflin, 1935; MIT Press,
1965).
  GK Zipf, Human Behavior and the Principle of Least Effort (Addison-
Wesley, 1949).
  GK Zipf , National Unity and Disunity: The Nation As a Bio-Social
Organism (Principia Press, Bloomington Indiana, 1941).

In spite of all the effort through the web, I can't find those papers.
I would be grateful if you could help me find those papers on the web
or get their hard copies by any means.

Thanks in advance for your help.

Regards,
C.H. KIM