Might look on this website. Met the guy at a gun show a few years ago. He's a police officer out of Plainfield doing this on the side. I like his products, but I'm not sure if he's got exactly what you're looking for.
A quick Go Ogle search turned up this ... https://slimriver.ecrater.com/ ... which is apparently the Malaysia company you referenced.
Their single point sling isn't all that difficult to reverse engineer if you study the pictures. They're using a small fixed loop to attach to the wrist of the rifle and a large adjustable loop to go around the body. The small loop has a disconnecting buckle at one end as does the adjustable loop. The two loops are joined together using a single triangle buckle.
This same set-up could be made using paracord instead of the nylon webbing.
Honestly, this looks like a great winter project. You should be able to find all the materials you need (if you build with nylon webbing) at Hobby Lobby or JoAnne Fabrics. If you go with paracord, then pick your favorite paracord outlet.