On your map, there should be a L icon, just like Leonardo's machines icon except that it's white, that indicates where you can find Leonardo. It should be one of the inventions that you can buy from him.
i only done 2 machines and bought all items i could so it would make sense, and what does playing previous games have to do with the leo system? it is new and nothing like it in the previous 2 games. unless ofcourse you mean "double blade hidden blade" which could indicate lack of brain cells, inability to explain oneself fully or a number of other thingsnot linked to previous games... --- Bad spellers of the world untie!