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.
