Donor milk is not an option beyond the current milk banks for sick babies. It's effectively asking mums to produce milk for two or more babies, theirs and a random baby. Even cows don't try and feed their baby and give milk away. Current farming techniques the calfs are removed at 2 days old, males are shot, females raised on a formula before switching to a feed mix.
The UK lost breastfeeding experience
and knowledge in WW2 & post war generations. The government pushed formula to get mum's back to work. They even produced National Dried Milk. Being able to buy formula was a seen as a status symbol, why go to the effort of BFing if you can affort to buy milk. All of that damage needs to be undone.
New mums are told breast is best, without real information on what breastfeeding is like. Struggling with a cluster feeding infant and you keep hearing 'I tried and couldn't', 'My GP told me I wasn't making enough milk to just switch to formula', 'I could help if you gave a bottle' etc.
It takes encouragement to keep going and not cave into the pressure. Much of my support came from a lady on another forum.
In some cultures around the world new mums only care for their newborn for first 40 days. The grans and aunties look after older children and run the house.
In the UK partly because of lack of BFing experience and knowledge new mums are expected to get on with running the house, shopping, caring for older children, doing school / nursery runs. But remember the newborn wants to feed during the night to build mum's supply. So poor mum's been awake half the night and still expected to function normally during the day. Then mum feel like failures and cave into formula.
So instead of thinking donor milk is the answer we need to be looking at getting proper support for BFing mum's to get themselves to the 6week mark.