Show the man at Pastoria City (near the Great Marsh) a Pokemon with max Smartness for a Green Scarf.
Source: Experience
In Pastoria City, when you talk to the guy, your Pokemon must have full smartness.
Feed your Pokemon poffins until it's smart maxes out.In a house in Pastoria city(i don't know witch one)talk to a women holding a parsol.She will give the green scarf.Works the same with other contest stats. Source: Experience This is Pokemon platinum's answer.Sorry for the inconvenience.