Buy one on the Grand Exchange for 201gp, or buy one from the bartender in yanille for 10gp. Another option is to make one. 4 clean harralander and level 29 cooking are needed.
Greenman's Ale is an ale that can be brewed with the Cooking skill at level 29, granting 281 experience, 4 Harralander herbs are needed to make this. Note: It can also be bought from the bartender in...