Primalists explicitly aren't able to take extra rage power (This ability does not count as the rage power class feature for determining feat prerequisites and other requirements.)
There's at least one magic item which gives specific rage powers, the helm of fearsome mien for the intimidating glare power.
You can take the Raging Blood feat, which grants you the 1st-level bloodrager bloodline power and counts as the bloodrage class feature. If you don't want to multiclass, you'll need the Eldritch Heritage feat as a prerequisite; Eldritch Heritage requires either Skill Focus or Exotic Heritage as prerequisite. So you're looking at a cost of 3 feats.
The Blood Vengeance or Sympathetic Rage feats give you a barbarian's rage; only available to non-lawful Orcs & Half-Orcs.
If you want a Totemic Rage Power, the Totemic Initiate + Disciple +Master featline can give you these, but only if you have no other totemic rage powers. You'll need the Athletic feat as a prerequisite.
Do you take your 4th-level bloodline power? Because sacrificing it would net you two rage powers, and you might be able to get a close replacement to the bloodline power.