All stainless steel made in Sheffield, England. Labour and Wait (one of my all time favorite stores and early ACL material) sells them, or you can get one direct from the manufacturer via their website. These knives are classic. Equal parts function and weapon. If you made a close inspection of The William Brown Project site, you would have noticed he saw them in London.
I suspect New York City police will not take kindly to their presence, but I suppose that just makes carrying one more fun. Same goes for the TSA, and no one wants to be on the full-body-cavity-search-list. [Update: British Military Knife $32 via Garrett Wade Thanks Tom]