How do you find single mode and multimode fiber?

What do you mean? You want to purchase optical fiber? Or you just want to tell the difference between single mode and multimode fiber? There are many fiber optic manfacturer around the world, in China I know a manufacturer called Ingellen Technology, a good supplier for most of my fiber optic related products. You can find various type of fiber optic fibers or plastic fibers there.
What i also want to tell you is that the endless stream of new technologies in the field of optical fiber communication, whether it is a long-range, high-capacity, or business, they are all developed for single-mode fiber.