If you want to get onto the shelves such as at WHSmiths, waterstones etc, then have a look at what is already on their shelves of similar book type, see who publishes it and make contact. A google search may reveal a website for the publisher and if you can get an appointment with there head purchaser and sell him/her the book, wet there appetite, then they'll be keen to put you forward to the major stockists.
Beforehand, it might be worth sending some samples to a book club and ask for written opinions so you can use this material to support your sale. It'd look good on you to have done some prep before getting to the publishers.
Good luck!!!
