Don't know how much luck you're going to have with that. The Soviets supposedly restaged the whole thing several days after the fact, based on a documentary I saw with one of the soldiers who was part of the actual flag raising. This guy was a bit miffed that they didn't feature the original soldiers but rather "recruiting poster" types for the cameras.
There was also a propaganda film shot in the late 40s or early 50s that shows the event, and it is supposedly wildly inaccurate. The movie depicts a pitched gunbattle at the doors of the Reichstag but the soldier said they were pretty much alone when they reached the building.
Given all that, I'd say that a few pictures of the building itself and some creative license will be as good as you're going to get, and with not too much work.