I saw one on another forum. Very pricey. I don't remember who made it, it might have been eglidegoodies. It had a shift handle on the gearbox that looked kinda awkward.
Of course, sitting there shuffling your feet in gravel because you can't back up could look kinda awkward, too. lol
AIM Corp makes a reverse gear for HD touring bikes. Harley should give the option for a reverse gear. That is my only complaint about these 800lbs bikes, it that they are hard to back up. I'm 5'5 with my boots on and I have a street glide and I got to tell, its a pain on a slight slope.