Depends on your luck.

A couple of my friends got him after 60 -120 pulls.

After 300+ pulls i still dont have him, but i do have mei.

A player once reported to have gotten the super rare (ay or susanoo sasuke) before getting mei. So about 850 pulls?

Every rare ninja you have a chance, but it is very RNGish.

If you want a surefire method of getting him then save coupons starting now. We are getting 20 Darui frags in 2 weeks time as sign in rewards. I'd be very surprised to not see him pop out in one of the events in the following weeks.