Part of the examiners' official role is to determine whether your thesis is a publishable piece of research. They will probably have told you either at the viva or in their written report what their recommendations are regarding publication. Publication in book form is not the only, or even the best route. In some areas, journal articles may be more effective: seek advice from your examiners and supervisor about this. Their recommendations are your first point of call and should provide useful guidelines when deciding what and how much needs to be rewritten.
Your examiners may well be able to suggests publishers with lists in your field. If they don't, ask them (given that they may be operating to a tight timetable, check when is a good time to go through this with them). This is the quickest and perhaps the most reliable route to finding a publisher.