Back in the early days, the GunZ was hosted by NHN’s own North America portal, Ijji. The portal later closed down, and most of the game went under Aeria Games’ stable as part of a deal. Fast forward a couple of years, Aeria has just announced the closure of GunZ: The Duel.
Most of the players are already waiting for the sequel, GunZ 2: The Second Duel, but so far there hasn’t been news for an official English server. Developer Maiet has placed the game on Steam Greenlight, perhaps in an effort to try and self-publish.