Janey - the eyelet was sold separately for the Singer and Greist sets. If you got one in a "set", they did not come that way originally. However that is how I've gotten all of mine, in with other stuff.
I've seen the boxes for extra singer sets and eyelets, and plenty of assorted 4 set boxes for Greist (and others made by Greist), but I don't recall ever seeing the box for a Greist Eyelet buttonhole.