The Kilrathi Saga manual lists "Planned 2669" as the service date.
Here are the descriptions:
Wing Commander Academy: "Similar to a particle cannon, this blaster also combines long-range effectiveness with powerful damage potential. Reaper cannon are even more powerful than neutron guns, but they also deplete blaster power very quickly. Currently in development for use on the new Confederation Wraith, these weapons represent our latest advances in blaster technology."
Wing Commander Armada: "The heaviest gun developed to date, the reaper cannon has gunned down more ships than all other weapons combined. Besides acting effectively at long range, this blaster has powerful damage potential and recharges quickly."
Wing Commander III: "(This gun will be available as soon as it completes its test cycle.) The RCX-V1 reaper cannon evolved from the standard ion cannon, and its refire rate is slightly faster. This gun delivers high-speed pulses of charged atomic particles that give off energy and radiation damage. Fighters find this gun especially useful against ships with shields that regenerate quickly, and any ship with slow shield generation is sure to take damage."