I have something that fits the bill. I picked it up from a forum member 2 years ago. Maybe someone can ID it, but unfortunately I don't remember which forum, or member, and I think this was a prototype to something that never went into production. At least I have never seen another like it. It WAS powder coated, but was flaking off so I painted it. Paint is not holding up well, but easy for me to do again.
I don't keep it on all the time. Just 2 bolts and it adjusts forward and back in the grooves of the aluminum rack plate.