I don't know where you might get one, but I can tell you what they were like.
Quite wide webbing, with the rear portion with an extra loop. A right handed shooter put his left arm through this loop and tightened a keeper on it, to make it tight on his upper arm. It was adjusted so placing the butt to the shoulder, tightened it right up, in other words, the loop hild the rifle butt TIGHT to the shoulder.
The lower left arm made a twist in the forward part of the sling, then the hand took a grip from under the forestock. When in the shooting position the rifle was held to the body like it was fastened on with screws and glue!
Shooting prone with this was almost as solid as resting over sand bags.
Too bad it is such a lost art that a shooter has to ask what the slings were like.