You can craft enriched dimeritium plates and ingots from enriched dimeritium ore. This in turn can be crafted from normal dimeritium ore + orichalcum ore + acid extract. All those components are fairly easy to find. How do I get enriched Dimeritium plates? how to get enriched dimeritium ingot.

Who can craft enriched Dimeritium ingot?

Armorer and blacksmith are the only ones that can craft stuff for you. There are 2 master craftsmen in the base version of the game. Armorer Yoana in Crow’s Perch, Velen and blacksmith Eibhear Hattori in Novigrad. The grand master items that appear in Toussaint can be crafted only in Toussaint.

How do I farm Dimeritium in Witcher 3?

If you find yourself lacking Dimeritium Ingot, it can be looted from dead bodies and chests or earned by dismantling weapons. Further, depending on where you are in the game, you can also get the Ingot (and sometimes Plates) by completing various quests.