Buying is always the easy way. Iron fence places often have a large selection of steel rings.

You can make circles with an ID just slightly larger than the OD of the drive roll. With a groove, you can make rings that can't be removed from the roll without springing them open a little. If you do a lot, you can add a motor and a foot switch. No idea of the quality or lack thereof on the HF unit, but I'm sure you can check it out in person to see. A lot depends on the finished quality of the rings you are making, as to the best way to do them.