The F-15 M9 locking block spring fits multiple KWA models, and appears on respective diagrams as M9 PTP & M9 Tactical PTP part 70, and M93R II NS2 part 108.
This metal spring fits the KMP9 and KMP9R and appears as part 162 on the KMP9 diagram. It connects to the KMP9 disconnector, part 153. Disconnector sold separately.