I have been wondering about this kind of thing too. My understanding is that it's fairly easy to print onto cotton. You can get special paper sheets that go into a home printer and can then be ironed onto cotton to transfer the image, for about £1 for an A4 sheet as I recall. I have no idea what the resolution is like but I suspect low.

I am in the UK and I am not sure how useful maps would be here. I know my local area already, and a map of the entire country would surely be too low resolution to be useful. In any case if I had to navigate across the UK I'd probably just follow the roads and trust the road signs. Or find a shop or abandoned house and search for maps in there.

The other issue with maps is that detailed ones tend to be local, which limits their usefulness. Other information might be useful to more people, and so worth doing a bigger print run for, which would make it worth using a better, more expensive printing system.