i suppose you know his head is shaped like Mount Youtei and that his name basically means "Fat Potato Boy". Jagata-kun is omnipresent in Kutchan, you shouldn't have any problems finding him.
i've added a "Jagata-kun Sightings" Google map that anybody with a Gmail account can add places to: ==> [url=http://niseko.us/fc]http://niseko.us/fc[/url] <== we'll see if anybody uses it.
also, this is at least 5 years old, but it is still kind of hilarious, if only for the production value: http://www.geocities.jp/waht0136/jagataop.html