Looks a good bit of kit .ive just went back to all leather slings on my own rifles the neoprene slings a crap never sit right in the shoulder .
I picked mine up from William Rollinson saddler from bridge of earn the man makes some quality kit ,he will if you have an particular idea will make it for you .
It's possibly an AKAH item, looks like one I have seen in a German Catalogue, both of which I have 'lent' and never got back so can't check for you!! Try checking Frankonia Jagd or Alljagd sport online. The sites are in German but if you find the search icon and search on 'Riemen' (sling) there will be a heap to chose from.
I'm pretty confident it will be there however I recon one of the leather boys on SD could knock you up one if you have no joy.
Bisley make a heavy duty leather sling similar to the one in the picture. Could also PM Dougster from this site as he was selling some bespoke ones recently.
Hot Dog that is the one i ment to put up any way its the one i use leather and webbing great sling.
Best sling ive had I made out of horse reins, get the widest ones you can, they stick to your shoulder like glue, stops modded rifle slipping around, rubber coated ones