You could try Conte's (the store) in Westport....203-226-3474. They may be able to help or at least point you in the right direction.
My other thought would be to defer to the lovely Ina Garten and make it yourself with her "Kitchen Clambake" Link below:
I guess I'm wondering why you need a package deal. All you really need to do is toss in whatever ingredients you want, sweet potatoes, corn, lobster, clams in that order giving the ealier ingreds some time to cook before adding the next ones, toss in some butter and boil them up. It's really pretty simple unless you are looking for something that has some proprietary seasoning or something along that line, but you can also get creative with that if you want.