Greetings from Solveig!
> I wonder how someone up in Avacal of An Tir get a hold of one of
> these books...
The An Tir Principal Herald may have a copy. Most likely whoever is
responsible for external commentary will have a copy. That is part of
the point of the "No Photocopy List". Various resources are widely
owned by members of the College of Arms. If you have a particularly
cooperative acquisitions librarian nearby, you can try to get them to
order a copy for their library.
Your Humble Servant