For those that are up to speed, the final dragon tear can easily be found below the dead dragon near Forgotten Caverns. If you have yet to progress this far, continue playing the campaign. The final dragon tear cannot be found until after Kratos and Atreus make their way back to Thamur’s Corpse as part of the main story. This talisman, with its devastating blast ability, is definitely worth upgrading, so finding that final dragon tear is essential.
Upgrading the Shattered Gauntlet of Ages for Kratos to use requires three of the legendary dragon tear resources, and though finding two is easy enough, finding the missing third dragon tear can be difficult.