EDIT; i have found the undercity quartermaster so there is no need to answer the question.
so I’ve found 3 horde quartermaster vendors in Orgimmar (darkspear, orgrimmar & bligewater cartel), i am revered with all 3 and have bought each of their unique bags which have 16 slots, is there a 4th quartermaster that sells the same bag once the rep is reached? or is it just those 3?