You'd be surprised at the number fake "antique" handcuffs aold on eBay. Almost anything sold as slave irons or Old West or with the name of a famous prison are fake, particularly if they have a brass tag proclaiming their provenance.
There are real ones out there, too. I believe Michael has a set of rather unique blacksmith made leg irons for sale now, and I've bought a couple of pair that actually appear genuine.
There's an excellent eBay guide to handcuffs up. It was written by one of ours.
Ones like you have are seldom faked, as it would be expensive to make fakes, except for incredibly rare stuff. Most of the fake stuff comes out of India and Pakistan, and are recognizable at 1000 yards once you've seen the difference. There are innumerable cheap "Official Police" cuffs up. I call them "Party Cuffs," as that's about all they're good for, and they're not much good for that, either.