First: you should contact the school property. Otherwise, you can't set up a stall.
Second: You should make a phone call (phone number can be found online) to negotiate with the manufacturer.
2. 1 you say you have this idea, then ask the other party's wishes, and if you want to cooperate, then talk about the details of cooperation.
2.2 Before negotiating with the manufacturer, try to understand the market yourself, otherwise you will lose a lot.
2.3 cooperation is generally in the form of low prices.
Third: You should also make sure that your things are liked by students and competitive.
I hope you can adopt it. I did the same thing in college.