If it was load that you were carrying you could simply stack dental bearings along the shaft. So I assume that you need bigger bearings because you are transmitting torque along the supported shaft through the centre of the bearing. Power = torque * RPM, so by using higher speed you can reduce torque for the same power, which reduces bearing size. Ball bearing RPM is inversely proportional to diameter. At 200k RPM with a 10 mm diameter, bearing surface speeds will be around 360 km/hr. You are getting too close to the edge of the envelope for reliable cool intermittent operation of ball bearings.
The bearing operational envelope decides what is available. Bigger dental bearings will not need to be made if there is a better bearing technology for those dimensions. Each technology develops it's niche, there are so many dental bearings made that they have finally optimised the design. Dental bearings are not rated for continuous operation at those speeds. Outside the dental sized ball bearing there will be very little experience and so they will be unreliable. It will depend on the duty cycle and longevity you require. I suspect you may be looking at speeds and powers that will require either magnetic bearings or bearings separated and cooled by hydrogen gas pressure.
There is also the problem of balancing the rotor and of rotor vibration. Magnetic and fluid bearings have a much greater tolerance for rotor asymmetry than do ball bearings.
Without a better idea of the application, power and geometry, it is hard to narrow down the search or invert the design.
