CP/M source code (v1.1, v1.3, v1.4 and v2.0) is avalaible at the Computer History Museum
-The Computer History Museum let you download 4 versions of CP/M for a non commercial use : v1.1 (1975), v1.3 (1976), v1.4 (1978) and v2.0 (1979), but it was v2.2 which was available for Amstrad CPC.
Gary Kildall, the creator of CP/M is sadly not anymore with us since 1994.