Homes Good Furnishers, Frohilde Snow-Hair (EP), Maladdiq (AD), Rohzika (DC), and Krrztrrb (Belkarth, The Hollow City), are co-located with Achievement Furnishers. They are marked by a chair on the map and this banner in-game.
The Mastercraft Mediator, Rolis Hlaalu, is located in the Alliance Capitals of Elden Root, Mournhold, and Wayrest. He sells some plans directly for Writ Vouchers earned through crafting Master Writs. You can also purchase the Hlaalu Furnisher’s Document for 10 Writ Vouchers. These contain random furnishing plans.