The parallelogram V-brakes already mentioned are Shimano XTR M950 and 951 and Avid Arch Rival. They are all a tad bulkier than regular V-brakes, so they may interfere with some other hardware on the bike. They must be hunted at eBay and may cost more than when they were new.
I was helping my kid with his homework learning the shapes - square, rhombus, right triangle, etc. When we got to the parallelogram, I proudly showed him the parallelograms shifters on his bike.