Genuine coins from the period chronicled by Tolkien would indeed be "ancient" -- haling from the Third Age of Middle Earth (the
Greeks and
Romans lived in the Fourth Age, as do we). I have encountered these coins on
eBay, but always passed them by as modern
fakes, as they appeared to have been machine made, whereas the genuine coins of the era would, I assume, have been struck.
Given their fabled skill as metal workers, I would imagine that the
quality of coinage struck by the dwarves would have been quite impressive.