Pumpkin Seeds are planted in a garden bed, 4 to a bed, with Farming mastery 12 for plain seeds (14 and 16 for the better grades), the highest of any garden crop. A harvested bed gives seeds back along with its Pumpkins.
The town Vegetable Stand sells them from tier II (5 in stock, 20 at tier III). At the Millstone, 4 pumpkin seeds of any grade press into 2 Seed oil.