All the sites in the book are on this site. Every site on TMA, which has a grid ref (all the ones in the book do), also shows the long/lat. Here's Mein Hirion http://www.themodernantiquarian.com/site/127

The problam with the grid refs in the book is that Julian has a strange aversion to the letters! Don't know why he does this, but it's rather bloody annoying. This makes converting the refs from the book very difficult unless you know which letters prefix them.

It may be better to go to eash page on this website and copy them from there.