As far as I know, apart from the Heinemann textbooks and the Edexcel past papers, the best resource available would be:
B. Jefferson and T. Beadsworth, Further Mechanics, (Oxford University Press, 2001). ISBN: 978-0-19-914738-0
It's pretty definitive and can be used for all boards. I think it starts from M3 and goes up to M5 but you'd have to check that.
P.S. physicsgirlie, you might want to try this out too!