The thing is, finding an individual blacksmith can be tough without the original connection. I suggest to look at online retailers who specialize in historical reproduction hardware. There are some who often cater to reenactment communities or traditional leatherworkers. Companies focusing on rendezvous and Old West supplies, as well as sites that host many small makers, like Etsy, frequently carry hand-forged iron pieces, including d-rings and square buckles, which usually have that distinct, rustic finish you are looking for. You can also try searching for custom blacksmith shops that take on small orders for hardware coz they are the people actually producing those items.