The method used in Mourning's End Part I. Requires a bucket of water, a bear fur and 2 silk. There are 6 pieces in total.
Kill a level 11 mourner at Arandar, west of the outpost (easily accessed with a necklace of passage) and pick up the mourner clothing and gas mask.
Note: When you start the battle, the mourner will throw a potion at you that will reduce all of your combat stats including Hitpoints and Prayer to 20. The only teleport you will be able to cast is home teleport.
Travel to Taverley and steal Tegid's soap from his laundry basket south-east of the circular building.
With a bucket of water in your inventory, use the bar of soap on the bloody mourner top.
With 2 silk and a bear fur, travel to Lletya and speak to Oronwen in the crafting shop, and ask if she can repair your trousers. (3)…
3
I have all I need to mend my trousers
After completion of Song of the Elves, the gear can be obtained by searching the chest in front of the burgundy-coloured bed under the Mourner's Headquarters.