First time I did this quest I farmed wildlife for a hour straight and only got 1 on the first hellboar I killed, I decided to run back to the ledge and use it, logged back in the next day and got a gland on my first kill, Since then I always get a gland run it to the ledge and so on and the gland  drops either first or second kill, try it out and see if it works for you too.