I have been looking for decent black olives in the UK for ages, just like the ones served in the restaurants over there - nice dark black & shiny, not like the Greek kalamata ones which are widely available here but rather brown and not the same thing at all.
Anyway, if anyone is interested and still reading this, olives from Turkey are for sale in Tesco - from Turkish company Durmaz, £2.45 for 300g - very nice, and healthy too