Large pieces of slim slate (Hook KT9)

I would love to make a rockery using several large pieces of slim slate, something in the region of 20 to 40cm long and 10 to 20cm wide, but not too thick - maybe 2cm/3cm thick. I can collect from Chessington, Surbiton, Thames Ditton, Tolworth area only. It's a long shot, but hoping someone has a few unwanted slate pieces kicking around. Thank you.