Teaching Resources for English 3API teach Eng 3AP Language and Writing and need sources of professional criticism for non-fiction. Can you refer such sources?
If you haven't attended an AP Institute (week-long, in the summer) you should most definitely look into it. It will absolutely transform your teaching of an AP class. If you are looking for information about the test, released test questions, etc. the college board web site is loaded with things for teachers to use. If you go to your local book store you can find some credible resources that are readily available to students and teachers such as Cliff's Notes for the AP Exam, How to Crack the AP, Five Steps to a Five. The books all have their strengths and weaknesses, but there is usually something worth considering. Lastly, I would suggest reaching out to other teachers of AP in schools local to you; you might be surprised at how hungry we AP teachers are to just bounce ideas off of other teachers who have the same big looming test at the end of the year!
I agree that the AP Listserv is great. enotes also has excellent resources for different books. For most of the major works there is criticism available. There is also criticism for authors. I also suggest Prestwick House's AP units, which are available for nonfiction. You can get them under lesson plans here or I think also in document exchange.
Have you joined the listserv? Go to the college board website and sign up for the free listserv which is packed with helpful tips and resources almost daily.