I second the above post. I searched several used book sites a few years ago, and while the novel (also called "Do, Re, Mi"
was readily available, there was never a listing for the show.
Maybe Tams Witmark has a script that you could ask to peruse to decide if your little theatre group (that doesn't exist) would want to do the show. Then you take it to the office, take it apart very carefully remembering where the pieces go, make a copy and then reassemble the script.
While this isn't exactly kosher, you'd get the script.