Coins can be found anywhere. I once found a 1925 English shilling in the middle of a crop field. On Time Team, a gold sovereign was found in an old moat. But coins collect where they are used. Locally, in what was once the Roman town of Durocornovium, unusual groups of late empire coins were discovered. What had happened was a change of architecture had led to wooden huts raised on stone plinths, so coins were being lost through the floorboards. Or in the case of Cunetio, a Roman town next to modern day Marlborough, a substantial buried hoard was found, presumably belonging to someone who meant to come back and recover his loot. OR more generally, used as offerings in lakes and rivers.
I suppose really you find coins whereever human beings have been, the amount and disposition depending on the circumstance.