It seems like people should have already made this. It is just a chain that snaps together. You can glue the ends or the hole should be large enough for a 6mm magnet on the ends if you need the chain able to break. I made it as a prop for drama.

Update: I changed the size of the hole to fit a 6x2mm magnet if you need to break the chain. I also included a spiked section.

The way I would print these out is laying on their side. If it's a regular chain I would print whole chain then chain link then back to whole chain For the spike I would print the "Spike full" then "Chain link" then "Whole chain" then "Chain link" and repeat for as long as you need. I would suggest against the spike link just because it has more room for error.

Happy printing