It's kind of hard to see because the picture is small, but here are some that come in a box that says "stainless steel handcuffs".
They can be bought here:
http://www.gunsamerica.com/996309416/Non-Guns/Tactical-Equipment-Vests/Stainless_Steel_Handcuffs.htm
It still makes me curious. The thing is, I'd imagine teenagers getting handcuffs for sex play from a place like Spencer's Gifts ... more novelty items, if you will (like with fur, etc.). Spencer's also carries nickel-plated ones for $9.99 (http://www.spencersonline.com/product/metal-handcuffs11/). I suppose some kids might order them other places online, like the example.