Place 1 cup corn starch in a bowl; set aside. Combine bread crumbs, 1/2 cup corn starch and coconut flakes in a separate bow; set aside. Combine 1 cup pina colada drink mix, powdered sugar, and rum in a separate bowl; set aside. Coat shrimp in corn starch, then dip in pina colada mixture, then in coconut mixture, back into pina colada mixture and back into coconut mixture. Carefully drop each coated shrimp into 375 degree oil, fry until golden brown; drain on brown paper bags. To make sauce, combine 1/2 cup pina colada drink mix, sour cream and pineapple. Dip fried shrimp in sauce.