So I really wanted a c-loop or similar strap system for my cameras because having the strap connect loosely to the bottom of your camera is totally the best ever, especially when you have to lug around two bodies with big lenses all day!
I took a trip to the hardware store and voila! problem solved. All you need is about five bucks worth of stuff: metal and rubber washers, a 1/4” eye bolt and some kind of locking or spring loaded chain link or carabiner. Throw it all in the bottom of your camera and attach your favorite strap and thats it. One of my cameras has the original Nikon strap attached to the link and the other has an old guitar strap.
The only thing to watch for is that the bolt is short enough and you have enough washers so it has the tension to keep from unscrewing (thats why the rubber washers are important). And if the bolt is to long or you don’t have enough washers and you screw it in too far you can mess up your camera! If the bolt is way too long you can cut it down to size.