Here is a short video about where you can buy a number of shirts from a vendor in Dalaran, these shirts are used from transmog. I leaned this tip from Jim from Power Word:Gold. This is not going to be a massive market, but I find these market kind of fun, because I love it when people buy my items of the auction house that you can buy from vendors!!
I hope you enjoy the video and start to make gold from selling these on your realm. Please leave a comment about how they sell on your auction house i.e. price and volume sold, as this might help other people get more of an idea of prices.