It is for sale commercially. Hella expensive! $107 for 50 ml.

innov-research.com/…/single-donor-human-breast-mi…

Now you can get it from private individuals for less - a buck or two per ounce, plus overnight shipping. But there are no food safety guarantees. You have no idea who the donor is, what kind of diet they have (may be an issue if you have food or drug allergies), or their health. That’s why it’s not recommended by the FDA.