Hi

So I know that some upper year courses are not offered every year and that they alternate every other year. So I was wondering how I can find out which courses are alternating or not? Is there a list of those courses somewhere or something?

Nope.

Usually if a class alternates it's because there a) isn't a prof to teach it (non-tenured) b) tenured profs who can teach it are too busy or c) there isn't a lot of demand for it.

You can ask your department when they've offered the course in past years, but all that can really be is a guide.