You can white label your own shampoo, sunglasses, supplements, anything, and even if you do the sometimes quite hard work of making sure your product is world-class, it often still doesn’t change the fact that once you have the product in hand, you’re now in the marketing business. This holds true even if you’re tapping a captive customer base with demonstrated search intent as in the case of Amazon. High quality product helps, but in the end it’s a marketing business.
This site doesn’t appear to make things much easier than just googling ‘[x product] contract manufacturer’ and picking up the phone. The product is the easy part.