Schools and colleges simply don't have the time and resources to find placements. As an example, when I was teaching I had to find a two-week work experience placement for a single 15yo pupil (who had actually been the only pupil in the class to find his own placement but which had unfortunately fallen through). I had to make over 230 phone calls before I could find a suitable placement for him.
Similarly, a 17yo friend of mine was seeking a 2-day per week work placement in order to complete his plumbing course. He didn't know where to start but I drafted a letter for him, which we sent to 53 different companies, enclosing s.a.e's for replies (with me paying for the 106 first-class stamps).
Schools and colleges simply have neither the time nor the money for such tasks, so you need to start by finding the names and addresses of all potential employers and organisations and then drafting a suitable letter to send to each of them.