Why not write them a note telling them the above (i.e. it's the best thing you ever had) and would they possibly part with a recipe as to how they did it. Hard to duplicate a restaurant recipe but surely worth a try. It might not taste the same w/farmed shrimp....assuming they used a Gulf shrimp which is mucho mas mejor. Perhaps a good reason to go back.

Buy a dozen clams, open, and save juice. In a large pan, add 1/2 oil and 1/2 butter
scallions and garlic. Saute' shrimps on very high flame and turning immediately for few minutes. I prefer to dislay them on a platter, add chopped parsley, assemble the opened claims, add a little seasoned breadcrumbs and parsley. Pour the clam juice over them. Broil for 5 minutes.

Blackened seafood is a technique that was developed by Paul Prudhomme in New Orleans. You season the shrimp with a special seasoning blend of usually salt, pepper, paprika, dried thyme, dried oregano, and sometimes cayenne. Some recipes also call for onion and garlic powder. It's tricky to blacken at home because it requires a cast iron skillet and extremely high heat. Higher than you probably want in your kitchen. And you can use a grill, but you also have to be really careful not to overcook the seafood. You could probably get similar flavor from using the seasoning blends and grilling on both sides, then finishing off in a garlicky sauce. My brother-in-law does this; in fact I just posted his recipe:
http://www.food52.com/recipes/9106_davids_hot_and_spicy_shrimp_with_pasta

And here's some more info about blackening:
http://www.ehow.com/about_5271565_blackening-seasoning.html