Hi Ray,
The pizza stone I bought from a local "Kitchen Stuff Plus" - I'm sure there's something equivalent in the UK. It was about $15.
The key is to get the oven as hot as possible. Mine goes to 600 degrees fahrenheit, and the naans cook in about 2 minutes - I'm sure close to a tandoor.
The recipe I use exactly as stated, except omit the additional baking powder.
-- Josh