As Annabelle points out the practiclness of it is not there. Humans do not make enough milk to mass produce it, and it would more like slavery to produce it. Cows produce sometime 2-3 gallons of milk each, twice a day and there are literally millions of cattle across the USA to produce enough milk to supply the market demand.
Besides the thought of the taste of human milk on my cereal in the morning sounds disgusting... It's more like sweetened condensed milk in taste.