I can see a few potential problems here.
1 - cost of molds for something that simple
2 - LOTS of finishing labor cutting sprues, sanding mold lines, etc.
3- the rings will just NOT be as strong as ones made of wire
I would think you would be better off finding or making rods/bars
for wrapping them around to give consistent results and speed, and
keep doing it the way you are. Just try to organize the work in a
way to maximize production and invest in the necessary tools and
machinery to do it. Tumble finishing, solder filled wire are a
couple that come to mind. Good luck Jim