Is it acceptable to ask for course notes ahead of time?
I suppose there might be exceptions, but I think in general it is fine to ask. But explain your reasons as you have done above. On the other hand, don't expect that you will necessarily get anything back. Many people create the notes on the fly as needed, rather than in advance. That will depend on the course and the lecturer. 

In my case I prepared a set of written notes that were printed and bound. Students purchased them for the cost of preparation. But I seldom had them available much before the start of the term as they were updated for each running of the class. 

Often the class notes aren't a lot of use without the lectures they accompany, so you might not get as much out of them as you hope. The lecturer will probably not be happy with you if you also ask a long stream of questions about them prior to the course.

I doubt that many would consider it inappropriate or giving yourself an unfair advantage. Most would appreciate your enthusiasm.