If you were super keen to avoid plastic, Lidl do tins of powdered milk, and you could reconstitute at home
Do they do that again? They stopped selling it around here - it was (and still is) my standby as I don't have a fridge!
To illustrate how stupid the entire system is: When I was at college (about 12 years ago now), I lived on the college farm. To buy the organic milk that was produced not 50 metres from my bed, I had to walk 3 miles to Tesco's and buy what had been carted down south several 100 miles for processing and then carted back up to the shop...
I know people who have organic raw milk sent up from England (to Aberdeenshire), with ice packs to keep it cool. Must be incredibly expensive, but then some people seem to have money to spend...