Your school will have a placement department that will know where the interns are going most often. I recall there being an intern or two at all of the flight test departments l worked for, but don't get hung up on flight test only, ask for any aircraft internship you can get for now and go do it. You really are joining a company in the larger sense, no straight out of school engineer knows anything very specialized in the beginning so it does not matter what you do. The real learning takes place on the job, college serves as our basic foundation on which to build a specialty. If you can get an internship at say, Lockheed doing stress analysis, go for it, and while you are there, ask about the flight test department. For that matter you could also intern at an airline like American, they have large flight sciences department. I actually interviewed for Delta at one point for a job with their performance group in Atlanta, and I have had pals who learned a lot about flight sciences working at places such as FlightSafety (the simulator firm), American Airlines, Spirit Aerosystems, and so forth. If you really get stuck PM me, and I will dig up the list of aerospace firms my college gave everyone in aerospace school to use for job hunting.