After years of working and collecting all the equipment and fabric for my retirement of quilting, I ran into the very same problem. In fact one project lingers on the edge of the long arm. I don't remember where I bought these, but they are off. I need to make a quilt that uses them up.
Marcia
P. S. There is a huge volcano going off near Mexico City here on 5-18-17 6 a.m. EDT.