What I did was start wearing a chain necklace with a Miraculous Medal – that way I singularly fulfilled the “requirements” of both the Montfortian and Militia Imaculata devotions. So, I technically cheated!
I think, though, that de Montfort is literally asking us to (optionally) wear an iron chain! So much for looking fashionable. :rolleyes:
Seriously, though, if you want to be as literal as I’m sure de Montfort intended, you could go to your local hardware store and buy a length of actual chain with small, unwelded links, pry two links apart, and connect them like a bracelet, anklet, or necklace.
Another option, though, which is much less literal and a bit more fashionable, is to Google “chain link necklace” and see if you find something which you like. I’m sure if *you * (being a woman) bought a man’s chain link necklace (or whatever) then that would probably be just as penitential as wearing a piece of logging chain.