Oh, you edited your post after I replied. Anyway, my point about the uniform still stands. It's a modified version of a real uniform style, so you probably wouldn't need to get one made from scratch. Wikipedia says that the overall style of the outfit is modeled after the
Gakuran-style school uniform, and the jacket is an extra-long
happi, so you could probably find patterns for those on a cosplay site, and modify their measurements based on the official art.
Hope that helps some.