What kind of JST connector will fit this stepper motor?
I don't see the reference to the S11B-ZR in the datasheet you linked. It is possible that not all contacts in the 11 way commector are populated1. The datasheet should be clear which contacts are being used.  

The S11B-ZR has a 1.5 mm pitch, so a 2.54 or 1.27 mm contra-connector won't fit. You might want to cut off the original connector and solder it to a connector of your own choice (keeping the voltage and current rating in mind).

1) For high voltages, it is possible that only pin 1, 3, 5, 7, 9 and 11 are populated in order to create creepage distance. But I wonder if that is the case in your stepper motor.

EDIT
If you want the best datasheet, you need to search the manufacturer's site.
I didn't find the MY7001 you linked to, but did find the MY14HY7 which seems to me very similar.
If you look closely to the picture in the right upper corner, it reveals how the leads are populated in the housing: on positions 1, 3, 5, 7, 9 and 11.
BTW, the MY7001 states it has 4 No. of leads...