He hired someone statewide 2 or 3 days ago. The slates of delegates have to be submitted 3 weeks from tomorrow, and he has to find 338 delegates/alternates in that time. If that was statewide, it wouldn't be a problem, but they will have to go district by district to find 3 delegates and three alternates that can afford the $900 participation fee (that the campaign cannot pay for them) as well as the $3000-6000 cost to attend the convention, and are registered Republicans living in the district. In a lot of these districts, there may one be a couple of thousand Republicans living there, and a lot of the districts are lower income (South Central LA, central valley, etc.) So it will be a challenge for them.
I think this guy Manafort has a good handle on it. Trump is well on his way to 1237 which is really the only thing that counts. Speculating about second ballot voting is fun but not going to happen. I believe Trump will take CA.