The OWB will be fixed inside the chuck shaft. Then I'll cut a shaft for it. One end of the shaft will go into the OWB and the other end will be fixed to the motor shaft with a pair of set screw.
There are some on here that are good up into the 10's of thousands of RPM's. I did not look for anything for your particular application. I personally like Zero-Max servo class couplers for my servos, they are top notch but I did not see any rated over 10,000 RPM this morning. But I also did not look at all the offerings. The Zero-Max servo class couplers are a similar design to the ones in this link.