Chitin is a fairly common resource used in Ark. Harvested from various creatures, this substance is used in armor and cementing paste, as well as the crafting of other items. It is far more common than most might think. You just have to look in the right places!
Chitin is harvested from a few Dinos. The Scorpion is one of them, along with the various flying insects. However, the most abundant source of Chitin comes from the Trilobites. These things are found in good numbers along or in most rivers, along the coast and in the sea.
They are tough-skinned and run when attacked. A Spear or Pike is recomended. Keep in mind that when harvesting Trilobites I have found it next to impossible to harvest them with a Hatchet or Pick.
By harvesting the Trilobite, you can easily rack up enough Chitin for a bunch of Cementing Paste or Chitin Armor. They also drop Oil or Silica Pearls along with a bit of Meat from time to time. But be aware they do not always drop Chitin. You can also get Chitin from the various Ants you'll find.