"Shrimp boats is a comin', their sails are in sight", but not within a thousand miles of Boston.
When you say shrimp will be served at an event, most people think first of the large shrimp served whole as a shrimp cocktail or on a salad plate. These shrimp are caught (and usually farmed) in the Gulf of Mexico, Thailand, China, the Phillipines, and Central America. They are almost invariably shipped frozen and then sold frozen, thawed, or thawed and cooked.
In my experience, it is always best to buy them frozen, thaw them slowly at home, and then cook them in small batches until they are all finished. This way you are most sure of consistent excellent results without undercooking or overcooking any.
For events, I always buy the Contessa brand 21-25/lb two-pound bag frozen. I thaw them for two days in the refrigerator, then I cook them a dozen at a time in a big stockpot at a rolling boil. They take only a couple of minutes, and start to float when done. If you add too many cold shrimp to the pot, or if you use too little water, the water cools too much and takes too long to come back to the boil.
The only food shrimp local to New England are the little red Northern Shrimp, known to us as Maine Shrimp. These are caught fresh off the coast of Maine, NH, and Massachusetts, but by far mostly in Maine. These are sometimes available in grocery stores as cooked, shelled salad shrimp.