I've been one of those women, but this isn't a consideration I will randomly hand out to women who are finding breastfeeding challenging.
Milk from milk banks is generally limited in availability to babies with special medical needs, and only available by prescription, which you won't get unless there are special medical needs, because the supply isn't great. Depending on your insurance, you're likely to have to pay for it as well, and the last time I heard a quote (~7 years ago) it was $3/ounce - that's more then my entire family grocery budget.
There are some donors who will trade for cheap - I donated my milk and asked nothing but storage bags in exchange. However:
- The reason I wasn't giving to a milk bank was that I couldn't meet their standards. I'm on anti-depressants, and I lived in the UK during mad cow. If you're concerned about pasteurization or impurities, you probably want to stick with the milk bank.
- The reason I was donating AT ALL was that I had massive oversupply that never entirely resolved. I was pumping 16-20 ounces twice a day until my son was a year old, and he reverse cycled in daycare and did most of his eating at night. End result? I was putting 27-35 ounces of breastmilk into my freezer every day. The problem was slightly better with my DD (NICU baby, I stayed home longer), she ate about 40-50% of the pumped output from 4 10-12 ounce pumping sessions per day. The people who took my donor milk got a *lot* of foremilk, because I saved the better blended bottles preferentially for my own kid. Foremilk/hindmilk imbalance causes foamy diarrhea in newborns, and foremilk is way lower in calories. (I did warn them. An all foremilk bottle is very watery, almost light green in color. I can tell when I pump it, but not when I freeze.)
- It may take multiple donors to get enough milk to feed your baby, and those donors are likely to have different diets, some of which may cause problems. Plus: extra errands.
- The people I gave milk to drove up to 50 miles each way to come to my house at my convenience and get breast milk. You probably need a car, and you have to be able to match the donor's schedule. Especially if you need multiple donors, this is a major logistical undertaking.
- Some people do find the whole notion creepy, and you have to be sensitive to that.
If breastmilk is *really* important to you, and you can find a source that you're comfortable with and can get to, donor milk is an option. In any other circumstance, combination feeding or straight-up formula may be preferable. When I needed to stop pumping for DD, I chose formula, despite knowing that donor milk was available, and how to find it. And honestly? Formula while I worked and nursing at home was amazingly easy for us. (I wished I'd been able to do it with DS, because it would have meant a ton to my career to not spend so much time locked in a closet, pumping milk my baby was largely not even going to drink, just to avoid leaking and pain.)
Unless someone has expressed an interest in donor milk, or has a particular special need, I just don't make that as a recommendation.