Here's how I made mine.
I went to Home Depot and looked for the largest washers I could find. It might take a while to find these, so ask someone if you can't find the big ones.
Cut out circles of fabric. I'm not really quite sure how big these circles are. I used flannel to give light padding and to make it a little more non-skid. Just trace around your washers, giving enough seam for the width of the radius. This gives enough room for the fabric to wrap around the edges and meet in the middle. Doesn't make much sense, me trying to explain it, so hopefully the pics will help.
Hand-sew a running stitch all the way around the edges. Place the washer in the center and pull the thread tightly.
I ended up stitching thru close to the original stitching line, reinforcing it before I knotted.
You can use more than one washer, or mix 2 washers of different sizes.