OD here http://www.militaryinsurplus.co.uk/Vests/Harnesses/Snipers-Waist-Pack-OD/prod_510.html but out of stock
Airsoft Forums UK
Lozart
Lozart
Scratch that - Helmetworld have them in stock! http://www.ebay.co.uk/itm/AIRSOFT-EMERSON-LIGHTWEIGHT-TACTICAL-SNIPER-STEALTH-WAIST-PACK-BELT-TAN-KHAKI-/390858475330?_trksid=p2054897.l5659
SimonQuigley
That one from helmet world is quite a bit more expensive 
Lozart
You want to buy it in the UK, it'll be more expensive. Simple. Also it's the same one but with a different brand, which again may push the price up a bit.