Kevin Brownlow's book, 'The Search for Charlie Chaplin' is available at a couple of online locations. I have been in contact with a few people who ordered from both sources and received their items, but I have not ordered personally from them. Both sources are in Italy, where the book was produced and release July 2005. You can order through Le Mani (details at chaplin.com). The other source is libreiauniversitaria.it.
If ordering from the states or Canada, do expect it to take sometime and figure in the exchange rate for the full cost. No word when this book will be available in America or the UK for those who like to wait. See this review from Chaplin fan Rainer Mann about the book. Rainer writes on a forum at comedyclassic.org.