Where can i find a Treadmill for Racing Horses that will exceed 40 MPH or 1:40 min/mile?

I have been looking at some horse treadmills for sale on the internet, and to my disappointment have discovered that even the so-called "high speed" treadmills only go 16 MPH as their fastest speed setting. that is insufficient for my purposes. I need a horse treadmill that will achieve full gallop racing speeds, that is about 40 MPH or 1:40 min/mile. Where can i find one of those horse treadmills?