If you go to craft, then you can create an objective for the item you want too craft. Like stun arrows require stone. Best too find them near rocky areas or riverbanks.
Create an objective and then they will show up as markers if you are near to them. This is a great way to learn what certain items look like, and eventually you will spot them without the need to create an objective, although it can be really helpful when your really looking for certain ones.