Find the grandmaster smith in beauclair first, you'll need him for crafting this special set since it's only available through blood and wine. The diagrams are spread around toussaint, start at bastoy prison ruins northwest of the city for the steel sword, then check the cave past trastamara hunting cottage for the chest piece. Only comes in grandmaster quality and needs level 40, no lower versions exist which is actually pretty nice since you won't waste materials on upgrades.

Make sure to grab both quests while you're in beauclair, "scavenger hunt: grandmaster manticore" and "master master master master!" since they connect to getting the diagrams. Really strong set for alchemy builds, helps with toxicity and gives good protection against most damage types. Good to know if you've got the complete edition you already have access to this, just need to reach toussaint first.

Check the grandmaster smith's requirements before hunting the diagrams since crafting needs some rare materials, and don't forget this is medium armor so plan your build accordingly.