I agree with the others here. It is very difficult to get a book published in the world of ESL/EFL/ELT, for the reasons already mentioned.
I can recommend an excellent book on getting a book published (covers everything from book proposals to contracts to self-publishing). It’s called Putting Your Passion Into Print by Arielle Eckstut and David Henry Sterry. I found it so helpful, I have already bought two copies.
My first book, The Creative Classroom, was published a couple of years ago by Lynx Publishing out of Canada. It was a lucky break, especially since it was a teacher’s resource book, which typically sell far worse than student’s books. However, they’re not interested in my second book, so I might end up self-publishing it. Anyway, you might try them. Their website is www.lynxpublishing.com
Other ESL/EFL publishers include Cambridge University Press, Oxford University Press, Helbling Languages, and Delta Publishing. In Taiwan, Caves Books, Crane Publishing, and Bookman Books all publish some ESL/EFL titles.
Self-publishing is another option (read up on it in Putting Your Passion Into Print). I know a teacher who paid $300 U.S. to get an ESL conversation book published by Booksurge, and was making a profit within just a few months.
Also, Alex Case over at the TEFL.NET website has a good article on getting published:
http://www.tefl.net/alexcase/articles/elt-publishing/publishing-tips/