In a food processor, combine the shrimp, eggs, lemon zest and garlic. Pulse until the shrimp is in small pea-sized bits and the mixture looks like a thick paste. Add the flour, cornstarch and ½ teaspoon salt; pulse, scraping down the sides if needed, until combined. Add the corn, scallions and celery. Pulse again a few times to combine.
Line a baking sheet with paper towels. Fill a large frying pan with about ½-inch worth of canola oil. Heat over medium-high until it reaches 350ºF. Scoop ½ cup of the shrimp and corn batter and place in the hot oil. Use the back of a ½-cup measuring cup to press down on the batter to spread it to roughly 5 inches in diameter, which is about ½-inch thick. Fry until very crisp and golden brown, about 5 minutes per side. Transfer to the paper towel-lined baking sheet and sprinkle with flaky salt. Repeat with the remaining batter.
In a small bowl, whisk together the mayo, Old Bay spice blend and lemon juice. Serve the Old Bay mayo with the warm fritters and dressed salad greens.