Dulwich Centre Publications in Australia openly advocates this therapy. It is also quite OK to use Wikipedia's entry for Narrative Therapy as one starting point. You can supplement its information with futher searches in major databases, even looking up any authors or researchers mentioned in that site, especially in the list of references at the bottom of the article.

Possible databases to check would be Psycarticles (full text database), Psycinfo, or even Academic Search at academic libraries, and Masterfile or Infotrac at public libraries. For free online sources, you can search Usa.gov which gets 66 hits for the phrase "narrative therapy". Usa.gov includes a number of state government sources, as well as Federal government reports and websites.

For additional "official" and some highly technical information, try Pubmed, which gets 32 hits for the search: "narrative therapy". None of these are full text; if you click on the "Limits" button to the lower left of the search screen and choose "links to free full text", the above search gets zero hits. But the 32 hits do have abstracts, which will help explain this therapy.

Trying to use Google Scholar to get full text scholarly articles can be quite frustrating if you are not at a library that subscribes to the many full text journals that Google Scholar indexes. To begin with, a search such as: "narrative therapy" introduction gets a whopping 2000+ hits in Google Scholar, and very many are books and articles that are NOT free full text on the web. Probably it is easier to try Google's web search, where "introduction to narrative therapy" site:edu gets 9 hits. Google Books "Full View" search gets zero hits for "narrative therapy" or "narrative therapies". But there are hundreds of hits for those searches in "all books", so you could find titles of books that you could then search in your nearby academic library - or even in Open Worldcat, if you are not near an academic library and have to rely on interlibrary loan from your local public library.