It wasn't a question of getting uranium, but of being able to moderate and attain a critical mass. In order to have a fission weapon, one must have either enriched uranium (very tedious and expensive process) or breed plutonium. Heavy water was one means of making a reactor using natural uranium, and is so used today in the CANDU reactors. The other approach was to use graphite, but that is not necessarily easy to come by in a wartime environment. We used graphite-moderated reactors to obtain the plutonium for the Fat Man bomb. The destruction of the heavy-water source put an end to the German bomb program. The program was also compartmented into about half a dozen sub-programs, with no overarching direction. Typical Nazi program proliferation, leading to waste and confusion.

I read about the supposed Japanese program, but the evidence only supports an attempt to do something, not that they had progressed to anything real. If they had, then it would have been reflected in the Emperor's understanding of what happened at Hiroshima. It took Nagasaki for him to believe that the atomic weapons were a serious matter. How is this delay possible, when his experts should have been able to confirm immediately what they were facing? And there was no evidence of any atomic explosion in Korea. Rumor is not fact.