nightstalkerpoet said:
The only official film sequel to The Wizard of Oz is an animated film. There have been quite a few remakes and different takes on the story, but nothing that touches on the direct continuity of Star Wars.
From what I have read, Return to Oz (1985), starring Fairuza Balk was supposed to be a direct sequel to The Wizard of Oz. It may not be complete, but it is taking elements from book 2 and 3.
By the way, while looking up the movie on IMDB, I came across the following:
"Director Walter Murch invited friend George Lucas to visit the set one day. During that visit Lucas wandered to different sound stages where he came across producer RickMcCallum working on a small film. The two became friends and later collaborated on the "Star Wars" prequels."