How about instead of rare resources being directly visible on the ground or in specific locations that everyone knows where to go, instead we have a divining rod and find them that way?
Toolmakers could make it.
Then the rares could easily be rotated dynamically as they dry up.
Perhaps there could be visual cues as in 'likely to find resource A in groves of trees' instead of flat out placing them on the map.
Just a thought.