Hm...Unfortunately I can't remember where exactly it was. All I remember was I was on a building that I would say was about medium height? As in, it wasn't a wire on top of those very tall pillars or tall rectangular buildings but more like a building that was half that height. I was shooting along a rail that went through a tree and when I got on the other side of the tree there was a coin JUST to my right in a patio type thing. (The area in the buildings that you can just fit into with the railing so people can look through the town.) Those are the trickiest ones I think.
Other than that, even though you have one coin left, if you are really struggling I honestly would say make a new file and check off EVERY coin you find with the online maps and I promise you, if you play just a decent amount you can finish it in about 3-4 days. Probably faster than just searching for one single coin. I was doing that for months =/