Dimeritium plate is a crafting component in The Witcher 3: Wild Hunt that can be dismantled into dimeritium ingots.
In the base game it must be crafted, but with the Blood and Wine expansion it can also be purchased from the following merchants:
- Armorer in Hauteville
- Blacksmith in Belgaard Manor, after he is rescued
- Lazare Lafargue in his workshop
- Trentin in his workshop in Hauteville
Crafting Requirements 
It is needed to craft almost all superior and mastercrafted witcher gear chest armors, in addition to a few more items:
- Impera Brigade armor
- Superior Feline armor
- Superior legendary Feline armor
- Mastercrafted Feline armor
- Mastercrafted legendary Feline armor
- Superior Griffin armor
- Superior legendary Griffin armor
- Mastercrafted Griffin armor
- Mastercrafted legendary Griffin armor
- Manticore armor
- Manticore boots
- Superior Ursine armor
- Superior legendary Ursine armor
- Mastercrafted Ursine armor
- Mastercrafted legendary Ursine armor
- Superior Wolven armor
- Superior legendary Wolven armor
- Mastercrafted Wolven armor
- Mastercrafted legendary Wolven armor
- Forgotten Wolven armor
- Legendary forgotten Wolven armor