This just popped up on my Facebook feed. I was a Girl Scout for about a week so I could go to camp with my cousin Mary, but my mother was a die-hard Scout for fifteen years. My brother considers himself a third-generation Eagle Scout because Mom was a Curved Bar (highest rank at the time) and her dad was an Eagle.
Anyway, Jo Ann Fabrics posted a .pdf on how to improvise an original 1910’s – 1920’s Girl Scout uniform using New Look 6004 for the skirt and Simplicity 8523 for the top, with long sleeves and middy color self-drafted. It does say that this project is “Level 3: Experience Necessary” as it’s a little bit complex.

It might a be a fun project for avid Scouters out there, though.
Here is an authentic uniform, circa 1925, on at the Minnesota Historical Society.
This photo is labeled “mid-1920’s” but it looks closer to late-teens/early 1920’s to me.