Ummmm.....
Three gun is an individual event. One shooter at a time on a course of fire. If you want to form a "team," that's fine, but good luck getting everyone to decide on the same "bowling shirts."
There's always a bunch of guys who like to squad together for any given match, and as far as I know, most matches allow that. Bring your buddies and have a good time hanging out on the range. That's what it's all about. If matching shirts make it more fun for you guys, then go for it!