One of the best places to find the publishing company of a book is to go to Amazon.com and type in the title of the book. The site gives the publishing company's name, the year it was published and a brief summary of the book. You can also go to Google Books (www.books.google.com) and type the title of the book. The page will show the name of the company as well as a link to the company's website to purchase the book.
Read recent book reviews. Most book reviews in magazines, newspapers and academic journals often include the book's publishing companies at the top of the page.
Look on the second or third page of the book. You'll often find the name of the company here. Sometimes you'll also find the company's website where you can find more books you may be interested in. Also look on the back of the book.
Go to Google Scholar. This is an especially good site because it will list the book you're interested in and lead you to Google Books, which lists the name of the book's publishing company.
Go to your university's library. The library's online and regular card catalog systems will have the name of your book's publisher, as well as where to find that particular book in the library.