In Mhaura, find an old woman named Vera looking out to sea. To unlock your Support Job, you'll have to bring her three items: a Bloody Robe, some Dhalmel Saliva and a Wild Rabbit Tail.
All three of these items drop from monsters right outside Mhaura's gates in Buburimu Peninsula; powerful ghosts called Bogies drop the Bloody Robes, the giraffe-like Dhalmels drop the Dhalmel Saliva and Might Rarabs drop the Wild Rabbit Tail. Note that, being undead, Bogies only appear at night.
Since people generally choose not to fight for experience points in Buburimu Peninsula, this will likely be the more time-consuming option.