Making Memories do a selection of metal tag rims. You get a template in the package to use for cutting your paper to size/shape. You slot the paper inside the rim and then squeeze it shut (they sell a tool called a Tag Maker designed for the job but you can run it through a die cutter like a Big Shot or Cuttlebug and achieve the same thing). The tag rims are on the Making Memories site
here if you want to see if it's what you're thinking of.
You can do the same thing with tag rims you purchase that have paper in them already - just ease it open (slide a pokey tool or the tip of a scalpel -with care!- in there to help you get started). Then use the paper insert as the template for your new insert and use your die cutter to squeeze it back shut.
HTH!
Metal ring tags
