These merchants can be found in the large cities: London, Paris and Beijing. They will offer you components for crafting - the smallest assortment in London, the largest in Beijing. Their prices aren't low but they will help you safe a lot of time and some of the "grind". So go and check them out before getting weary from collecting hundreds of materials. You can get monthly quests only from 25th to 27th of a month, and also only after completing at least two weekly quests the month before the 25th day. There are 6 different monthly quests and they will earn you big money.