I ship frozen milk all the time. Look up modern milksharing on Facebook. They give great suggestions for how to do it with videos. If you don't already, start freezing your milk flat. Makes packaging and shipping so much easier. Also if you don't want to ship, you can always post on human milk 4 human babies or eats on feets (in your area). There seems to be a shortage of donors lately.
PS. Shipping costs are the responsibility of the recipient not you. You package the milk and bring it to the UPS/FedEx store and call the person. They give their payment info right over the phone. It's pretty easy. Also you should ask for milk storage bags in return. Most are willing to send them seeing you are doing them such a huge favor.