The usual way to get footwear prototypes (especially in the categories you describe) is via a factory sample room.
But you can only do this if you can convince the factory that you will place production. They will not entertain anyone who is just wanting ‘look see’ samples. If they are not convinced by you (especially if you are not ‘trade’) then they will say no. If you make samples and don’t place production then there is no way they will do anything for you again. It’s a great way to lose a great factory IMO.
So the only way round this is to find a shoemaker, get him to make the uppers for you and then look for a model maker who can make you a model of the outsole. You can then ‘sit’ the lasted upper (called a pullover) on the model outsole for an idea of how the finished model will look. I have done this many times when working for brands over the years.
We have model makers in the UK who do outsole models, perhaps someone in the USA might know someone who can do outsole models. They need to be able to understand footwear, because they will need to know how to work with a last (making allowances for the lasted uppers etc). The British guys that I have used have all had long working relationships with famous footwear brands.