The Tir Tairngir sourcebook gives you the basics. You get some news about political changes in System Failure. There's a bit in Shadows of North America. You also have a mention in Sixth World Almanac, I believe. There's also some mentions in supplements like the Seattle book (since TT is next door), and the Spy Games, Dirty Tricks, and so on books, since they deal with spies, politics, and such. The Clutch of Dragons and Storm Front talk a bit about it, because of Hestaby. Land of Promise gives you the update on TT in general.