There is a web site at http://www.geocities.com/olmorijo/ Which contains the full text of the Thompson Book at: http://www.geocities.com/olmorijo/thomson_preface.htm
The site hasn't been updated for some time. And I've sometimes been unable to access it because it runs out of data transfer quota. But if you get in, you will also find copies of several interesting Maasai related documents, including
An Administrative Survey of the Masai Social System by H. A. Fosbrooke from Tanganyika Notes and Records, December 1948, Number 26.
Vocabulary of the Enguduk Iloigob by Revd. James Erhardt
Maasai Agreement 1904
Maasai Agreement 1911
High Court Judgement - Maasai Land Case 1913
Die Völkerstämme im Norden Deutsch=Ostafrikas, Kapitel VI., Die Masai und Wandorobbo von Max Weiß. Pp., 317- 410. Verlag von Carl Marschner, Berlin, 1910.
Book ID 264