Go for the anti-burst from Paintman Panels, they're very good. Paintman also supply barrel/key sets of you're still wanting to just change the barrels.
www.paintmanpanels.co.uk
MTC6506 Land Rover Antiburst Doorlock Barrels and keys is a 5 barrel lock set with 2 keys. Ideal for the front side doors and rear door of a Defender
www.paintmanpanels.co.uk