Manila Clam can be found in New Horizons. You cannot order it from the catalog.
mY FaVoriTe fLavOR of CLam iS mAniLA : r/AnimalCrossing
Browse catalog Animal Crossing Database and Wishlist Maker - VillagerDB
Animal Crossing Database and Wishlist Maker - VillagerDB
List of villagers by internal name (Animal Crossing), Animal Crossing Wiki
Clam - Animal Crossing: New Leaf for 3DS Guide - IGN
Shino Animal Crossing Database and Wishlist Maker - VillagerDB
Hop Along
Giant Clams and Villager Photos! : r/acnh
Toolbox Animal Crossing Database and Wishlist Maker - VillagerDB