Thanks for the clarification. I apologize for the delay in getting back to you. I'm on Eastern Time, and I had already gone to bed when your message came in.
When you said "vendor's license," I thought you were referring to the license you would need to legally sell items at a fixed location. Your local government officials, e.g., county auditor's office, would issue a vendor's license, not the merchants themselves.
At any rate, you do not need to have permission from Ralph Lauren, or GAP, or Banana Republic, or any other name brand manufacturer to purchase their products wholesale and then resell them. So long as you are purchasing the items from an authorized wholesaler (who must have permission from the manufacturer to sell the products) what you are doing is perfectly legitimate, and you need no permissions.
Again, the reason for using an authorized wholesaler is to ensure that the products are legitimate and not knock-offs, since it is necessary for the wholesaler to have first obtained the manufacturer's authorization to sell/resell its products.
Hope this helps.