Are ultra high racers available commercially?
This is a low racer:

The frame goes lower than the wheel's axles, and as a result the rider's shoulders are somewhere near even with the top of the wheel.  In extreme cases, the rider's head looks to almost rest on the back tyre.  It can be very hard to see forward from these positions, but its the most aero.

This is a high racer:

The lowest part on the frame is above the wheel's axle line.  Rider has a better view forward, but has a higher frontal area to catch the wind.

I'm not aware of anything higher than the high racer design.