Somewhat confusing question

I was playing on a pserver, on which I am allowed to use commands like spawn and give ad what not, but I keep seeing people with enemy projectiles as their weapon, like it will show up as the missing artwork symbol, but shoot that shot. I have seen people with the scarab shot, the O3 blue and red projectile, all those. Is there a way I can do that myself, whenever I ask on the server they avoid my question.

So basically if I want to use whatever weapon they are they would have to tell me the name or trade it to me? Ok then.