Have you asked him? If she's at your school, then why not just introduce yourself to her? If he's said that he won't introduce you, then there's probably a reason - maybe he likes this girl?
http://answers.yahoo.com/question/index;_ylt=AoxoASe5wOWwKJ.LAhAfIvbsy6IX;_ylv=3?qid=20100206010216AAnXW8u