Most complementary therapists, or practitioners of complementary health care, have undergone some form of professional training and are registered (and insured for professional and public liability) through a regulatory body.
To find a practitioner, you can contact the relevant umbrella organisation that regulates the training and codes of practice for the therapy you are considering.
Most regulatory bodies should be able to provide a register of practitioners and a leaflet outlining the therapy
Look in your local telephone directory under the relevant therapy heading – e.g. under osteopaths, you should find contact details for the General Osteopathic Council, alongside the names of relevant therapists in your area.