You can go on the aamc website and there will be a link that will take to the different codes for schools. There are only a few non-aamc schools allopathic schools...I think that 600 is the code name for osteopathic schools though.
if you could post a link to where on the site would help a lot. ive gone through the site twice and found two things. A faq saying I could put down 6 non amcas schools and a dead link to some acrobat file talking about non-amcas schools.