I'm surprised none of the Nashville crowd has piped in. You might try facebook. One of the problems with foosball is that it's mostly played in the bars where the minors aren't able to participate.
If you want to take a road trip, the Kentucky State tournament is this weekend.
$15,000 Kentucky States,
Horseshoe Casino
Elizabeth IN Apr 10-12
Horseshoe Casino
11999 Casino Center Dr SE
Elizabeth,IN 47117
He'll be able to get into the tournament room but not the casino area. If you do happen to take him there, introduce him to the tournament director, Mary Moore. She'll get him started in the right direction. A lot of the best players are in Europe this week for the World Cup but there will still be some very good talent for your son to watch. Many of the players are willing to help him out if he's just willing to ask.