Bring the turkey stock to a boil in a large saucepan. Stir in soup, and season with poultry seasoning, pepper, seasoned salt, and garlic powder. Reduce heat to low, and let simmer.
Warm the milk in the microwave, and whisk in the flour with a fork until there are no lumps. Return the gravy to a boil, and gradually stir in the milk mixture. Continue to cook, stirring constantly, for 1 minute, or until thickened. Be careful not to let the bottom scorch.