There are some notes in addition to some exercises for various topics available.
In fact, the key issue in doing additional mathematics is to practise. "Practice makes perfect." It's an undoubted training technique to make yourself being familiar with different kinds of questions in various topics. I know it may be difficult for you all to spend lots of time in doing exercises. However, A.maths is such a subject that consuming so much time.
Fianlly, I hope you all can succeed in the coming public examinations!