You can just Google "kilt flashes" & get lots of hits. But I have made ribbon ones as per the instructions in the earlier link I gave. They are very simple & can even be sewn by hand. They cost pennies compared to purchased ones, & you can easily have a whole "wardrobe" of flashes.

On another note, after looking more carefully at Rick's method, I think that I would just sew or serge the strip of fabric (width of finished flash x 2 + seam allowances) into a tube, leaving a long thread tail for turning (trim the seam allowances to about 1/4" if they are wider than that). This makes all the stitches hidden on the inside. Press the tube flat with the seam in the middle back. Then you can turn down the top & trim the bottom just as Rick describes.

Sherry