Wouldn't someone in that town know who "the kid" working on the farm was? Shouldn't Jane be out interviewing everyone who lives/used to live near the farm?

I agree with Ben. At this point, it shouldn't be hard to find Red John. Think about all the stuff we know about Red John. He hung out at that house near the blind lady. He is not fat or soft. He is not short. We know who many of his associates are.  We know the times and dates of his murders. If his name is on a list, process of elimination should work like magic.