Ok let's get serious for a minute.
If you want these places to provide you parts, what you need to do is ring them up and tell them what you are doing, they will then decide to give you a discount off the product (a demo discount). It won't be a give away like you expect but they will do something for you, at the end of the day they want to sell parts and make money.
If you can't do the work yourself you then need to find a company that is just starting out and doesn't have a name for it's self yet.
Tell them what your doing and that you will promote their business and tell eveyone what a fantastic job they have done. They will then decide if 'your build' will give them the publicity and attention they want and do the work at a discounted price.
I am HKS dealer, if I said to them I want to build a car to take to the drag strip, run some quick times and take to shows. They would give me stock at a demo or discounted price. That's basically how it works.