Try Basspro Shops. Also, just put in your zip code and it list stores near you:
http://www.costadelmar.com/aidStation/dealerLocator.cfm
Martin Opticians in Needham is a "Premium Wave" dealer and have just about every model that Costa's make. I'm in the market for a pair of Costa's too so I've been doing my research and trying on a bunch of different models.