Graahk fur can be obtained by trapping Horned Graahks on Karamja. The fur comes in 2 varieties, tatty graahk fur and perfect graahk fur. Tatty and perfect graahk fur can be taken to the Fancy Dress Shop in Varrock to be made into various articles of clothing. The tatty fur can only be made into Graahk tops and Graahk legs and the perfect fur is used for the headpiece.
With the release of Summoning, graahk fur has encountered a change in price because it is a tertiary ingredient in the making of Spirit graahk pouches, used frequently in crafting Nature runes.
Players can also get them as a reward from Soul Wars by using the "Gamble" option. This will give them fur in quantities of 5. It is not suggested players use this function to get fur, because receiving a decent amount of furs is unlikely.
The chances of receiving a graahk fur or tatty graahk fur are completely random and cannot be influenced in any way.