I am as a HUGE fan of the series, but I also make/sell props so I've thought about this a lot. The advice I have is this: Steam punk google can usually be found cheap online thru hot topic, spencers, or another punk clothing line. The chest ring however is a different story; Your going to have to make it. They way I would go at it is Start by going to a hardware store looking for a cheap bendable (yet durable) think metal wiring, bending that into a ring, then covering with paper attacted by masking tape to get it to the size you want it. Then you could just pant it OR if you want to make it truely legitament; cover the ring with Fosshape or Wonderflex (fosshape is cheaper but harder to put on) other covers would be paper mache, I suggest only buying about a pound of material if going with the Mache.
Good luck on your cosplay! Hope this helps!
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