[Kazan]

Wrong. There are 1079 delegates left. The Cruz/Kasich tag team needs will likely need to combine for more than 530 delegates.

[CA Conservative]

According to the Chronological Cumulative Allocation of Delegates on Green Papers, 1489 delegates have been allocated through yesterday. That leaves 983 delegates still to be selected. Of that, 28 from ND, 37 from CO, 9 from American Samoa and 54 from PA will go to the convention as unpledged, leaving 855 pledged delegates available.

If you look at the RCP delegate tracker, they show 1526 delegates allocated leaving only 946 delegates still to be awarded. The only difference is that RCP shows CO as already awarded.

So both of those site agree that the number of delegates available lower than 1000. And in both cases, the number of available pledged delegates is 855. So Trump needs 564 out of 855 to be sure of a first ballot win, or 66% of the remaining delegates. If Kasich and Cruz get to 300 combined, Trump cannot get to 1237.