That version of the Cedar source was on a CD-ROM accompanying the blue-and-white version of this SOSP'93 paper:
Carl Hauser, Christian Jacobi, Marvin Theimer, Brent Welch, and Mark Weiser. 1993. Using threads in interactive systems: a case study. SIGOPS Oper. Syst. Rev. 27, 5 (Dec. 1993), 94–105. https://doi.org/10.1145/173668.168627