A boxed set of all four seasons plus the movie is being released on DVD and Blu-ray in Nov. and Dec. (depending on the place), but so far it hasn't been announced for US release. Only some countries in Europe and Japan.
You could hold out for a little while and see if it comes here, but I'm starting to doubt it. It's probably not worth importing because of the DVD region lock-outs and the fact that Japanese BDs are insanely expensive (over $200 a season).