Make your own. Get 50 Ohm coax cable, and build an attenuator that will be at the motor end. You sure don't have to worry over capacitive loading when measuring this system! So, a 100:1 probe would need a 4950 Ohm resistor, shunted by a capacitor that is 1/100th the cable capacitance. You can look up the capacitance of various cables per foot (or m) online. You must be VERY careful to make sure the 50 Ohm termination on the scope is always available, so I would recommend using an external 50 Ohm terminator at the scope end. Actually, this will deliver 9 V to the scope end, so most internal terminators would not handle that, anyway. The 4950 Ohm resistor would need to have a rating of 163 Watts! OOPS, looks like a problem!!! Maybe a 1000:1 probe makes more sense, that would give you 900 mV when the input is at 900 V. The resistor would need to be 99950 Ohms, and power rating of 8 W. That might be doable with a bank of 16 paralleled 1/2 W resistors.
Jon