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The chain is actually really easy to make out of solid copper grounding wire, which you can get from any hardware or electrical supply store. I think it's #6 AWG or similar, because that's what I had, though smaller diameter wire (#8 or #10 AWG) would have been easier to work with. Copper grounding wire usually costs $0.40 to $0.70 per foot; four feet should be plenty to make a chain 18-20 inches long, including the clasp.
I used a dowel as a mandrel for the round links and a yardstick as a mandrel for the long links. It's the same process you would use for chain mail links: you wrap the wire around the mandrel multiple times in a tight spiral, then slide it off and cut the rings apart. If you don't solder the links together after assembling the chain, you will want to file down the edges so they aren't sharp.
This is a great idea - thanks a lot for sharing!