Nice work.Rings and the Staple can be made from round steel stock.
The ring simply clamp the round stock to an appropriate size mandrel.
I used an old damaged large threading tap, the shank of it happened to be the right size to form the ring.
Then heat the round stock red and wind it around the mandrel one + turns.
Then hack-saw the 'ring' off the stock by slicing through the material where it overlaps itself.
I silver soldered (hard solder) this one together at the joint.
The staple is best turned on a lathe. I think I started with 1/4" dia here.
Turn the shape to allow for the U shape, the flared supports and the stub 'feet' that enter the frame.
Everything gets polished up nice and then the Staple spread open just a bit to allow the ring to be inserted. Then close the staple. Blue it or 'age it' appropriately before placing it in the frame.
Place the asssembly in the frame and stake in place from the inside.
This one is from a Marlin 1893 project.