Guild Wars 2

Greetings, Nercos

Where can i find sinister accessories or how can i make sinister accessories

You can craft exotics with Charged Ambrite, like so:
https://wiki.guildwars2.com/wiki/Recipe:_Charged_Ambrite_Orichalcum_Amulet

Or, if you want the ascended version, you can either buy them for laurels or bandit crests, or get them as reward for completing living story achievments, like so:
http://wiki.guildwars2.com/wiki/Plague_Signet_