That kit looks a lot like the old Mark 3 kits, which BTW also used the same type of bed rails. The thing thats missing if it's a genuine Mark 3 are the decals on the sides and tailgate, but the decals could have been deleted when new, or peeled off later, or the truck was repainted. Mark 3 went out of business a long time ago and I'm not sure where they sourced the fender flares and integrated side steps. I personally believe that they made them which means they will be hard to find.
The closest thing, other than the Mark 3 kits I've seen, would be the old Lund fenders and separate (universal) fiberglass side steps once offered by Lund, which I don't think they make any more.
Ed