Just reread your initial request and realized you're probably after something generic and (fortunately) simple rather than something specific to the harness or parts kit. Just a clip to hold the little harness in place and keep it from moving around?
If so don't worry with the bike shop. Go to Lowes or Home Depot or Ace Hardware or most decent auto parts stores. Probably even Harbor Freight. Pick up some stick on clips like those in the picture here.
They come in various sizes. Stick it on the inside of the bag. Then run a small wire tie through the holes in its sides and around the harness. Pull the wire tie snug and, voila, your harness is tacked down.
You're not even doing anything Mother Harley doesn't do. HD uses these same type of harness mounting clips in several locations. But you can buy a bulk bag of a dozen or so at one of the stores mentioned above for what Mother Harley will charge you for one clip. Just don't forget to pick up a little bag of small wire ties also.