I asked a young friend of my son who is currently attending art school for recommendations. He actually gave me a link to an article by a Director of Recruitment for UCLA.
Being you don't have art classes available in your school, the advice given to reach out in advanced to some of the schools you are interested in seems very wise. This will give you a chance to see what they may specifically want to have you include and also give advice on how to handle the absence of school-related work.
You may also want to look into available classes at a local community college or evening classes in the area or a arts center. Sometimes these classes can be free or relatively inexpensive and may give you the opportunity for class-driven projects to include in your portfolio.
Hope this helps