Thanks. The work, including the source material,
is available with a CC-BY-NC-SA license.
All the information about generating the map is here, which you can use
to generate images of any resolution, admittedly with some time and effort.
http://github.com/kriskowal/3rin.gs/
I'll make a point to publish an 8Kx8K pixel image, which I think is sufficient
resolution for prints 2 meters to a side.
I have reservations about selling prints myself until such a time as I can
acquire permission from the Tolkiens' publisher. I've made a note to send them
another letter.
Thanks,
Kris Kowal