This guide will help you farm the legendary weapon:
Bulwark of Azzinoth
First off, we will be required to port to Stairs of Destiny.
[Might and Magic] > Mission Area > The Stairs of Destiny
Find the NPC called "Honor Guard"
Accept his quest; so you can see the necessary materials to obtain the upgrades for Bulwark of Azzinoth
Your first step will be to go into Black Temple and obtain the 20 Bulwark(s) of Azzinoth from Illidan Stormrage
[Might and Magic] > Raid Instances > The Burning Crusade Raid > Black Temple
Once in there, head to Illidan. You are able to ignore all of the other bosses, and head directly to him.
After you have defeated him, you have two options - reset the raid and run back up to Illidan; or wait until he respawns
After you have collected the 20 Bulwark(s), your next step is to head to "Felwood" for Prime of Azzinoth
Below will be a map the mobs will be in the vicinty of the circle
[Might and Magic] > Worldmap > Azeroth > Kalimdor > Felwood
After you have acquired the desired amount of Prime of Azzinoth(s), your next step is to head to "Shadowmoon Valley"
You will require to have Herbalism before heading there, as Fel Fire is a herbalism related item
Below will be a map of each node present in the zone
[Might and Magic] > Worldmap > Outland > Shadowmoon Valley
The final step is to buy a bunch of Handful of Fel Iron Bolts from the Engineering profession vendor.
Congratulations, you've acquired @Bulwark of Azzinoth
Pick up the next quest in the questline and continue your journey to maxing the shield