If your school offers free exams/radiographs, I'd suggest posting an ad on craigslist. Then ask some basic questions like when was the last dental visit, do they think they have cavities, oral hygiene etc. I had a TON of screenings and managed to find a bunch of boards patients for people with that...
Young people make good interproximal lesions. Older people with no dental visits more then 5 years are usually pretty good for perio.
Good luck!