Personally from my experience with my Bison Mark II, I had better experience with a Kirby belt to work rather than a Oreck belt to work. I just used a flat head screw driver to lift the belt on the shaft due to how tight it was.
They may have produced that many but they certainly did not sell that many. There was a post from someone here years ago that had an entire van load of NOS Bison vacuums he got off a pallet, where on earth he found them I do not know.
For how seldom they show up I do not think even but 2% of that amount survive, as they were prone to breaking so easily.