if its any help, they did 2 sets of rules where they touched (albeit briefly) on war in the north. The first was the original ROTK rulebook released as part of the boxed set game back in 2003/2004 I believe? It had a few scenarios in the back detailing the attack on Lorien in particular (but also has a map with notes on the attacks Sauron made) & the other was 'Ruin of Arnor' which also took place in the north, but before the WOTR & focused on Arnor & the Witch-King.
If you look for the ROTK rulebook on eBay / Amazon it will be the one with Aragorn riding Brego and a load of minas tirith warrior models on the front, not the journeybook. Hope this helps