In my opinion a good leather sling these days is almost impossible to find. I don't like those wide fancy ones that have gun manufactures names carved in them as there to wide and stiff. Also don't care for the ones that are adjustable with 50 holes punched in them and a set of hooks to set in the holes. Years ago I bought slings that were made by "Hunter" and it had a hunting horn stamped in the leather. They were a double strap set up 1" wide nice soft oiled leather. Very durable, still using the first one I bought in 1971. I have 3 of them and can't find them anymore or anything even close. So for my latest rifle it was off to Tandy leather. I bought 1" oiled leather straps, picked them over for thickness and softness, and a bag of brass rivets that screw together. I never adjust a sling once it is set for the length I like. So once I had the length I wanted just punch holes and double rivet the ends onto the swivels.
So I would strongly suggest if you can't find what you like, make your own as it is not difficult.