The starting point for a search for Atlantis should be in Egypt, since that's where the whole hype started. Everything else is probably pure guesswork. For example, this theory of mine could be convincing if properly researched:
The Sumerians had a myth about a Great Flood, just like the people who believe in the Old Testament (Jews, Christians, Muslims). Some vague knowledge of this, combined with better knowledge of Sumerian or Mesopotamian cities could easily be the origin of the myth considering the facts that Sumerian/Mesopotamian cities were near or surrounded by rivers. This also supports the idea that Atlantis was built in rings, as the structure of a ziqqurat may imply.
Even the description of orichalcum is supported by this. I know that there is nowadays a definition of orichalcum, but I'm not sure if this is what was originally meant. It could either be amber -which probably led some to think that it could also be somewhere in the Baltic sea, but there was already amber trade several millenia BC- bronze, which originated in Mesopotamia, or even iron. Depending on when the myth originated, which probably no-one can tell as it's origin was likely oral tradition, it could even be simple copper.
I personally believe that the Atlantis myth is most probably a very obscured memory of something known or unknown to modern-day historians. It was already obscured by the time Plato wrote it down, although I believe Plato was responsible for some more misunderstandings.
The romantic inside of me of course wants to believe that Atlantis was the way Plato described it, or at least similar to that, but the realist knows that this is likely not the case.