Institutions like Embry-Riddle or Purdue have digital libraries with licensed maintenance training materials, including the FCOM (Flight Crew Operations Manual) which contains full layout diagrams.
Quality Flight Sim add-ons (like QualityWings 787 or the upcoming iniBuilds 787) ship with detailed cockpit layout PDFs. These are not official Boeing docs but are reverse-engineered to 99% accuracy.
Introduction: The Digital Revolution in the Flight Deck
Search the FAA’s Dynamic Regulatory System for "B787 AFM." Appendix 1 of most AFMs contains a general cockpit arrangement. While watermarked, it is legally free to view.