Who should I work with to develop customized protein shakes and collagen powder products?
The first person you should work with is a marketing professional who will help you do your research, strategy, and validation steps so you know what product to create, who will buy it, how it will be sold, and what people will pay.
Second, you can talk to any number of nutritional supplement manufacturers that deal with powders. They can put together whatever formula they're directed to. Arizona Nutritionals comes to mind, but there are dozens.
DO NOT start with the product, except maybe some samples, part way into your marketing validation.