I am in the beginning stages of a vending business. How do I write a proposal to put my machines in a college that hasn't opened yet?
Just tell your story, and tell the truth.
If they're going to decide against you because you're new in business, that's disappointing, but you can't get around it because the truth will come out. So tell the truth, but then go on to why doing business with you is a good idea.
And if the college doesn't want you because your business doesn't have enough history, at least this standard proposal will be a good exercise. You'll be able to use most of it again.