Peel shrimp, leaving tails on. Butterfly shrimp by making a deep slit down the back of each from the large end to the tail, cutting to, but not through, inside curve of shrimp.
Stir together coconut milk, cilantro, and lime juice in a large bowl. Add shrimp, tossing gently to coat. Cover and chill 30 minutes. Drain shrimp from mixture (do not pat dry).
Whisk together flour and beer in a small bowl. Combine coconut and breadcrumbs in a shallow dish. Dip shrimp into beer batter; dredge in coconut mixture, pressing onto shrimp. Place shrimp on a baking sheet; freeze 20 minutes.
Pour oil to depth of 2 inches into a Dutch oven, and heat to 350°. Cook shrimp, in batches, 2 to 3 minutes or until golden. Drain on paper towels, and sprinkle lightly with salt. Serve immediately with Maui Mustard Sauce.