There is a great guy just west of Fort Smith, AR (Sallisaw, OK) that is very passionate about 337's. You can find more about it in this thread:
http://www.337skymaster.com/messages...ead.php?t=4673
If you want a type specific certificate (ME limited to center thrust) there are a few folks splattered about the country. Besides the ones mentioned below, there is Brad Newman at Tiffin Aire in Tiffin OH. If you want to get up north, Doug Rozendall who is the Chief of Staff for the Commemorative Air force lives up here in Mason City IA and he indicated that he would be able to give me my center thrust rating if my original plans fell through (which they didnt). There are options out there, but you may have to do a little traveling. I didnt mind as it involved flying. So I trained in OK and then flew with my instructor to OH for the check ride and then flew home to IA the next day. It was a some good flying!
Opps....I see your wallet is full of certificates! Helps if I read the entire post......