George
Best places to find past papers are any of the schools which do CPL/ATPL groundschool courses. 43 Air School, FTC, Avex, Aeronax Academy, Central Flying Academy, they all have their own database of questions which they may be able to sell to you.
My advise, use these schools to contact students who have recently done the exams, and see what you can negotiate with them!
FTC questions are close to the real thing and also 43 Air School have a fair idea of what's in the CAA database. Can't speak for the others, also I did mine a few years back so things might have changed.
Good luck!
CM