$6.75 each via mail order, in black, brass, or chrome finish at https://www.wish.com/search/brass%20knuckles/product/5fec26bb74f63c270f576a70?source=search&position=12
Or if you want something a tad more expensive: McDaniel Knives McKnucks. I want the pair with the holster, but I couldnt carry them so they would be just a nifty looking toy.