John;
You could make this yourself, it takes a bit of patience but you can make the slide buckles etc. (Former 031 Canadian Infantry) using a soft brass wire or solder for the sliders and the sling materiel can be made out of surgical tape. I have had some success with using old audio cassette tape as well for the sling. But the surgical tape holds paint better and is definitely better suited to the task.
To get a smooth edge the best way is to cut the surgical tape on a piece of glass or a glazed wall tile. Remove the adhesive by dipping it in some acetone or varsol and rub the adhesive off with your fingers. Once this dries either airbrush or brush paint with a flat or semi-gloss black for "nylon" look.
The sliders are the tricky part of this excercise. There was an article in an older issue of FSM and in one of the Kalmbach modeling manuals that show pictures of this process, but here goes.
Draw the shape(s) of the slider(s) on a piece of wood (scrap of 2 X 4 is my choice) and place a nail or stiff wire at the inside edge of the rectangle and then at the centre of the opposite sides (should form a diamond shape of sorts) then do the same for the corners. All the pegs should be to the inside edge and keep in mind the thickness of the materiel you're using to bend around to form the slider.
Once this is bent you should have the rectangle of the slider formed. To make the center piece either cut and solder the centre piece on, or continue bending the wire around your mini jig until you have the completed slider.
Once you have reached this point carefully remove the slider and flatten the rounded edges of the wire with either a couple of soft hammer strikes or with a pair of flat pliers. Then prime and paint.
Once you've made a couple it gets easier and they actually can be made to work like the full size item.
I hope this will help and answers your question. I will see if I have the article still and scan the demo drawings.
Cheers;
Gregory