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There is a Google map of Portland that shows pianos that can be played by the public.
There is also a group that reconditions old pianos and places them in public areas for people to play, they have a map as well but I don't think all their pianos are on the Google map because they get moved around often.
Quite a few cites have the wandering public piano thing happening now a days. Who knows, maybe you have such a service in your area.