How to I reference lecture notes?

If I were in your situation, I would check with either the instructor to whom the paper you are writing will be submitted, or with a librarian. The instructor who is going to grade the paper will most certainly accept the advice he or she gives you, and you will not need to worry about being graded down for an improper citation. But if that choice is not available, a librarian is highly likely to have an answer for you. Librarians are experts at locating information of this type.