I'm not certain about physical film footage, but in the last few years there have been several thousand period newsreels and cuts of unedited film footage released onto YouTube for the general public to watch. The biggest two that I'm aware of are British Movietone, which has a playlist about Hiroshima and Nagasaki here and British Pathe, which has a playlist called The Things that go BOOM! and is, predictably, about bomb deployment.

At my last check, British Movietone have 500,000 videos and reels, spanning from 1895 - 1986, and British Pathe have around 85,000 videos, so there's a fair amount to choose from!