Isn't there like 100 people who already flex their guns making deathmatch videos in GTA W?
Anyway, I don't think this would work. Sure military, police etc could have a show to show off their cars, equipment and all of that, but a gun show with civs there wouldn't really make sense. I've not seen anyone role-playing a proper ancient gun collector either, that'd even be able to display something. Surely a event team held event or something as such would work, but that'd not make sense as well. + all the modding for guns for just one event wouldn't really justify it in the long term.