Hey Dillon its great too see someone of your age on here, I wish I would have had that mindset going into high school instead of coming out like I do now. For prototypes and plastic I would try looking on Alibaba.com. Ive used that site to find manufacturers for all different types of things. You would probably have to pay a sample fee but once you pay that the company will bend over backwards because they know you are serious about business. Although I haven't done anything with plastics on the website I am sure that you could contact companies and figure out exactly what you need to have a prototype made.
Hope this helps!