Check IMSLP. Depending on your jurisdiction (primarily Canada, where copyright terms are shorter), the file might be available for free. However, for most US and EU users, IMSLP will block the download for copyright reasons. You may find a "study score" preview, but rarely the full performance score.
Cathy Berberian Genre: Avant-Garde / Extended Vocal Techniques Scoring: Solo Voice Cathy Berberian Stripsody Score.pdf
A very specific request!