Maybe Roosevelts. But not sure they would have lobster, you might call first. I would eat at the Venetian Hot Plate if you get a chance. I don't think they have lobster, but it's the best place in town since the pelican closed. Inferno is also good. Same guy who owned pelican.
I've never heard of Port A being a lobster destination. I'll put a plug in for Beach & Station Street (Grill). Everything there is great. Get some dessert as well. Ask to meet the cook.
Call the Spaghetti & Seafood Works restaurant. Their food is excellent, but I don't remember if lobster is on their menu. Everything I've eaten there is delicious!