Breast milk has become popular due to both well-meaning (statistical correlation to everything from higher income to higher IQ) and mommy-shaming (if you use formula, you are a bad parent) groups that it may actually be putting more kids at risk.
If you simply can't express enough milk, or don't want the hassle, you may be tempted to buy breast milk online. Obviously the hope is you get a reputable source but if you do run into problems, Aoife Finnerty, adjunct at the University College Cork,
outlines the legal situation.