It's still such a 'minority' thing, no-one is going to find it viable to do minatures of soya - you'll have to carry some with you, or manage without, or with cow's milk, depending on your dietary / moral requirements.
I thought it wouldn't be viable to be honest. I do carry some with me, but it's only a problem when the weather is really hot. I can't drink cow's milk, because I am allergic to it. I start shaking almost immediately after drinking it!
I have seen flavoured soya milk in small cartons but not unflavoured, they had chocolate and either strawberry or banana, can't remember which. It was in home bargains.
Yes, I just meant for coffee and tea. I can now got to Starbucks, Costa and Caffe Nero, but restaurants don't usually provide soya milk, or any dairy alternative.