I have just managed to get hold of a lot of ncr20700b batteries. They are 15A 4250mAh capacity.
Other than building a big 24v power pack with them I am wondering which flashlights have tubes big enough to fit these?
Any 21700 flashlight.
For example, the 21700 FW3A.
EDIT:
Actually some 21700 flashlights are so narrow that they won't fit wider 21700 cells, so 20700 cells are a good idea. 
Sofirn C8F with the 21700 tube.
Nicer grip and better “balance” than regular C8s because of the slightly wider tube.
MOST flashlights that claim to fit both 18650 and 3xAAA with a holder will fit 21700/20700 cells as well. Especially the cheap ones, because they don’t care about a tight fit for the cell or a short/slim host body, so they’re generously sized. I also own some cheap flashlights that are supposed to be 26650 size, but they are so oversized, the springs barely compress and the cell(s) bounce around in the tube. Those would surely be long enough for 20700 cells. Just use a spacer tube, or some tape wrapped around the cell, or some other method, to fill in the gap between the cell diameter and the interior of the host.