If you want to become a dealer in say Canon or Nikon, you must call the regions regional offices. Set up an appointment with a sales representative in your area. He/she will then explain to you what it will take to become an authorized sales dealer of their products.
Usually there is a minimum amount you must buy per year. Be aware, if you do set up an account and dealership, you must purchase product on a regular basis or your sales representative will not visit you on a weekly or even monthly basis.
This is why you see distributors like International Photo Supplies and WYNIT. They purchase in bulk and then pass the savings onto small dealers so that they can compete with the Costcos, B&H Photo and Adorama.