Is it possible to get a list of everyone who graduated from a college in a given year/field?
Such data exists at the universities and departments. However, in many jurisdictions there are legal restrictions that would limit their ability to share it with you. There are also practical limitations: the departments want to keep a good relationship with their alumni. If the alumni get contacted every other week by someone doing a project, then that would be bad. 

So to get access to these data is hard work. You need to convince them that this is a serious project, maybe you need IRB approval. You'll need to find a way to use that list without violating the law. Sometimes this involves you don't contact the alumni directly, but the department does, who will sent you the annonymised results. All this requires quite some investment by the department, so what is in it for them? Maybe they want to add a module to your questionair?