This special merchants only appear at certain dates on different places in the housing zones. They give special quests for which you need the Aether gems you collect from killing the Audrias that you find in the housing zones and as reward you get random furniture or housing items. Also you will find some special vendors with some really expensive items so if you want to invest lots of money in your house this are the Shugos for it!
This are the locations for Oriel:
Locations for Pernon: