I was frustrated when I was looking for it, BUT then I realized I could look it up in cheat menu - NOT TO CHEAT, just to see what does it look like, so that I would know what am I supposed to be looking for. It really helped me and then I found it in the farm the proper way. It wasn't easy, but it was fun and I was glad that I resisted and didn't cheat, because I do believe that the point of these quests is to have fun in the first place. Just be patient and pay attention to every detail, examine everything, you will eventually find it.