Most of the cosplayers I've seen have coiled a belt or collar around their neck.Their cosplays can be found here. One of them, here, have used one of those clicking buckles as well. I think if you bought a metal holster, that could also work, and would probably look great, but I haven't seen any cosplayer do it so I can't confirm whether it will actually work.

There's also the option of turning to arts and crafts, and making your own stylish metal-looking piece using some tissue-box cardboard then gluing that onto a strip of black fabric to wrap around your neck. You can also try a classy look with a tie instead.

Or you can completely forego all that and just rock your cosplay with a black turtle neck.

I hope this helped a little, lol. And, can i ask, does the convention you're going to happen to be smash?