Combine the eggs, garlic, lemon juice and Dijon in a food processor. With the machine running, slowly pour in the olive oil in a steady stream. (After all the oil is incorporated the mixture should resemble a light mayonnaise. Season the mixture with salt and pepper. Remove the mayonnaise from the machine and place in a mixing bowl. Fold in the tomatoes, corn, and green onions. Place the tarter sauce in the refrigerator until ready to use. In a mixing bowl, combine the cornmeal and masa harina together. Season the flours with salt and pepper. Dredge a couple of oysters at a time in the flour. Fry the oysters in the hot oil until the oysters start to curl, crispy and golden brown, about 2-3 minutes. Fry the oysters in batches. Remove the oysters from pan and drain on a paper lined plate. Season with salt and pepper. Serve the fried oysters with the tarter sauce.