What to do if there is no book about a certain topic?
In reading the following, keep in mind that anything you can do personally will have at best a minuscule effect on whether such a book gets written, and you shouldn't expect it to happen anytime soon.  For all practical purposes, you should plan on having to proceed with your research without the aid of this hypothetical book.

My impression is that these books usually get written on the author's own initiative, perhaps prompted by having them see a need for such a book.  So 
I think the best thing you can do is to identify someone who you think could write such a book: someone who is a recognized expert on the topic and who writes particularly well and clearly.  Contact them and say something like: "I've really appreciated reading your papers on topic X, but it strikes me that there are no books that could give a comprehensive introduction.  Have you ever considered writing one?"

Unfortunately, your message alone probably won't do much, particularly because you are a grad student - these suggestions would have more weight coming from someone who would be recognized as a fellow expert.  Someone who is more deeply acquainted with the existing literature and its gaps.  But if the potential author starts getting a number of such suggestions, it might plant the seed that such a project could be worthwhile.  

Of course, writing a book is a huge task (thousands of hours, I'd say) which is poorly compensated.  Academic structures are such that researchers tend to have stronger incentives to write papers than books.  If the book is to be published commercially, there is the additional question of whether it will be profitable - even if the book is fantastic, if the topic is too "niche", there may not be enough potential buyers to interest a publisher.

I don't think that contacting a publisher will have any effect.  Again, the incentives are such that a publisher can't do much to encourage anyone to write a book, unless they already really want to do so.