As previously mentioned, if you're willing to shell out 8k (7k or so with perks to reduce costs), the merchant in the canyon of Hissing Wastes on the central western end is one of the best locations for end-game schematics. If you also have the "Short List" perk and some patience, that merchant will offer at times 1 special offer. This offer may be a Superior version of the "Armor" type for Battlemage, Prowler or Battlemaster (higher utility slots of the three main trees of generic armor). These will sell for 15k or so. The Keeper Robe mechanic, for elven spellcasters, drops from one of the High Dragons (Highland Ravager in Empris du Lion I believe, debatably the most powerful dragon in the game, but regardless highest level.). The Keeper robe is excellent on its own, but I do not recall if you can add any upgrades that will drop to it, which may make it inferior in your estimation. It is also elf-only. Same issues apply to Dalish and Templar armors.
Top-Tier weapon schematics are sold at the keep in Empris du Lion. With the "Short List," Yavanalis (Level 23 unique staff) sometimes is available for 15k. Its stats are comparable to end-game crafted staffs, but considered non-ideal by many players. The "Sulevin Blade" is created through a quest into the Cradle of Sulevin, and crafts a blade that is arguably more powerful than any 2 handed weapon you can create in the game, with unique abilities not duplicatable otherwise. Its stats are debatably non-ideal, but it is, without question, one of the most powerful weapons in the game and will hold its own in comparison to crafted gear.
If you do not like the "Armor" tree of schematics and prefer the Mail or Coat for whatever reason, you will be relying upon Tier 3 drops from high level chests. Zones for these include Cradle of Sulevin, Empris du Lion, Emerald Graves (particularly the mansion instance) and Hissing Wastes. It's a matter of luck to get them. (Or farming if you wish to learn those techniques.)