Paul:
I don't sea duck hunt, but I stayed in a Holiday Inn and have a bunch of friends who do. I tend to agree with the comments above. In addition to the safety factor, I think sea duck hunting is highly dependent on local knowledge. Knowing where birds are likely to be given the combination of wind, tide and weather is not easy.
That said, if you are set on a DIY trip, there is plenty of good public access to the coast in Maine. This link (
http://www.maine.gov/dacf/parks/water_activities/boating/public_boat_launches/google_earth_maps.shtml) should take you to a Google Earth image of the entire state that shows all of the state-owned or managed trailered and hand carry boat launch sites. There are also other sites that are private or town owned . Sorry, but I don't have a single source for those.
I'm not qualified to give you advice on best parts of the coast to target, but I do know folks who hunt the area around Saco/Biddeford, outer Casco Bay, the lower end of the Sheepscot, Damariscotta and Kennebec Rivers, Penobscot Bay, and the area around Deer Isle. (Lest anyone accuse me of spot burning, that highlights about 1/3 of the Maine coast . . . .)
Hunting is best late in the season when water is cold and conditions are difficult. Be careful, and it probably makes sense to plan for one weather day in every three you plan to be here. It's not unheard of to get 4+ days in a row when you really can't safely get on the water. Remember that Maine does not have Sunday hunting--but if you focus on southern Maine you could cross the border and hunt New Hampshire on Sunday. I've never heard anything about it, but I suspect the eider hunting out around the Isles of Shoals on the ME/NH border would be good. You'll need boat enough to get ~10 miles offshore to get out there, and watch the location of the state line, which cuts right through the archipelago.
Brad Allen at the Maine Department of Inland Fisheries and Wildlife might be able to provide some information to help you plan a trip.