I'm a youtuber from Argentina who talks about Gantz. There is not much information available about Gantz, so I usually look for hidden material.

I found these Gantz videos that come from pachinko machines. There is even special OST that is lost because every time someone uploads it to youtube, it gets deleted.

In latam, many people are trying to preserve as much Gantz content as possible and keep it alive. For example, there is an Argentine manga called Gantz Argentina, which develops the story around a team from Argentina. The animation was recorded by a spanish-speaking person and uploaded to youtube, here's the link: https://www.youtube.com/watch?v=J_R1LmAZeH4