Since you don't have a bunch of "sources of sources" -- just this one -- you have three easy ways to remain honest and give due credit. 1) Find a way to cite the notes directly as a reference, preferably before you cite anything you were led to by the notes. Directly quoting something is not a prerequisite for citing it as a reference. 2) As you suggested, put a sentence in the acknowledgements section. Something like: The lecture notes from Dr. Smith's course, "Alien Spaceships," were used to provide overall direction and as a source of references. 3) Do both, just to be clear.
- Find a way to cite the notes directly as a reference, preferably before you cite anything you were led to by the notes. Directly quoting something is not a prerequisite for citing it as a reference.
- As you suggested, put a sentence in the acknowledgements section. Something like: The lecture notes from Dr. Smith's course, "Alien Spaceships," were used to provide overall direction and as a source of references.
- Do both, just to be clear.