I found a good bargain in Wickes hardware store. They mostly sell in bulk, however tey sell slates in single and whats more, they give good discounts on broken slates, I found a few in our local store, even slightly imperfect will give you reduction. I asked if I can have it free, they still charged me for broken. I got exactly sized I needed and it is lovely quality, not too thick. Very pleasd with it. We had simlar discussion earlier this year, chack this thread out:
http://www.shelledwarriors.co.uk/for...t=41300&page=2
HTH.