If your still an Artisian, you can go to the Qeynos Harbor and talk to the Ironforge guy, he is by the ship hull. Once you talk with him you will be promted to choose your level 10 class. Note only the first conversation counts. You should not be allowed to talk to him multiple times, if you are picking again will cause serious proublems for your character, so dont try to change your choice. :)If you have already dinged 10, then you need to make 1 more item after making your choice before it kicks over. (It appears to check when you earn exp).
As has been stated below, There is 1 Wholesaler in each newbie area and 3 Workshops. Note that you do not have to join the ones in your newbie area, you can find one that is more suited to your needs in other parts of the city. You can make this selection after you have your class I belive.