If you talk to someone at your local fish store (LFS), they may be able to order some shrimp for you. I have had special orders made for me, and they don't even charge extra. Many times they stock what sells well, but often have access to other species and are happy to order them, knowing they are going to sell them right away. I've never tried that with a PetSmart or PetCo type of store.
Barring that, you can order shrimp from
Aquarium Plants, Pond Plants, Freshwater Aquarium Plant & Aquarium Accessories – Arizona Aquatic Gardens (or other places -- see EBay). You will pay a good amount for overnight shipping and there is a minimum for your total order.