Where can I get a good baking stone?

[digibouti]

I want to buy DP a baking stone for Christmas but I'm struggling on where to find one. I want a proper stone for baking bread, rather than a pizza stone.

I think one of the great British bake off people I follow on twitter suggested requesting / buying a sample of slate for this purpose. Don't know any more myself but may be worth googling along those lines.

The best one I've got by a mile is a wilkinsons marble chopping board with the feet taken off. Doesn't look very posh wrapped up though!

I can't remember what Richard Bertine suggests, but I think it's similar to the suggestion above, find a stonemason and get a slab of something?