My DD did her exam last year and managed to secure a place at a grammar school in London. My suggestion would be some independent school papers, as my experience of finding her papers shows me that independent school papers tend to differ in difficulty, as opposed to other papers like Bond and Letts which are grouped according to age. Some independent school have a higher academic standard which means the papers are harder, and some are easier. http://www.sevenoaksschool.org/y7downloads
The Sevenoaks School papers are medium-difficulty, I'd say. A really challenging on would be on the Bancrofts School websites, though I would not recommend that until the Summer Holidays-July/August. http://www.st-anselms.com/224/entrance-exam-papers
These are the St Anselm's College papers, also medium difficulty. Start with http://www.christs-hospital.org.uk/pros ... ssessment/
This is quite good for a start!
I think the best would be to find more on Google!