In order to get a random Tortoise you need to buy the Tortoise Egg in the Shop (section with a treasure chest) for 3 Tortoise Talismans or 99 crystals. If you need a certain Tortoise for your collection you can get it during special offer.
Common Tortoises:
You can grow the vegetables in the Garden Bed or get them for free in the Farmer’s House, Vegetable Cart, Mushroom Hut and also in the Estate (Zucchini), Bunnies’ Playground (Carrot and Cabbage), Bunnies’ Dwelling (Carrot).