If you are looking for a sweet breakfast, Quaker True Delights has chocolate and banana coconut. You don’t have to order a sweet sample, they also offer Cashew bar. Breakfast snack bars are becoming more popular in recent years, so you can even extend you free cereal samples search by looking further for “free breakfast snacks”.
Although categorized as “free sample for kids”, don’t let that scare you off. You can sign up and get free Cheerios samples, in addition to other goodies like Nestle’s hot chocolate drink.