Pretty sure nothing exists to do this.
I would do this;-
Make a base plate out of 6mm ally. Fix to bike using countersunk bolts so the surface is fairly flush.
Buy from a Givi supplier a pair of the `mushrooms` that they use on their plates and fix these to your plate (Might make sense to use the same spacing as Givi so your set-up could easily be adapted to take a Givi box in the future by adding the `triangular latch)
On your box, rivet or bolt some brackets with cut-outs to match the mushrooms. These would need to stick out from the back of the box and be flush with the base of the box which means they would have to be L- brackets fitted to the outside of the box.
Slide the box onto the mushrooms then drill a single hole through from the inside of the box straight through the box and the baseplate. I would suggest M10. Install nut and bolt through hole.
Job done, and all you need to do to is remove the one bolt to take the box off. so you would need two spanners. You could make it so you don't need spanners if you tap the hole in the base plate and install an M10 bolt from the underside and tighten fully with a grip washer. The bolt would then poke through the base of the box and you could use a butterfly nut to fix it. You may have to make the hole in the box slightly larger, or open it up a tad on one side to cater for the box sliding onto the mushrooms at a slight angle.
